Oh Sharon, I know that a dear baby can be exhausting!!! We love them so much, but they take a lot of our energy when they are little don't they? My dc all had reflux and were up many nights, which kept me up many nights - so I truly feel your pain.
I think you are right, it is time to put little baby on a schedule. You will know how to do this just fine as you have done it well before.

I think the toddlers are the bunch that can run the house - in fact, they can run the whole day if we're not careful. I've come to realize this after many times trying to read to my other dc on the couch as toddler tore through the room and yelled over me.

So, this last year, I decided to do 2 things -
1: Use all of my house to homeschool (at times to get away from loud toddler - we love him, but you know what I mean here)
2: Train toddler to be independent with a few things and put my schedule around him
When he was 1-2 years old, this is what worked...
I trained him first thing in the morning to look at books in his crib. Sturdy books - a bunch of them - with the lights on and the curtains open. He enjoyed this for 20 minutes or so, and I got showered and ready.
Then, we did set up a "happy playpen time". Through trial and error, I came to realize it was important I set up the toys each time for him, around the edge of the playpen, sitting him in the middle. Then pick them up every time, so each day he was getting into a "new" looking play area in his playpen. Tubs of toys with sturdy books and favorite sit-down toys were set aside for use only during playpen time (I stored them in tubs under his crib; he has a very tiny room

). We put Christian radio on quite loudly. It worked the best in his room with a child protector doorknob cover and the door shut. This worked great for about a year (then he started crawling out). He started out doing this for 15 minutes, and then gradually happily played longer, like about 45 minutes. I taught like crazy downstairs during this time with the monitor on.
He also had a 30 minute playtime with older brother (8 yo) in the basement in an area we set up with a gate as a playroom. We did this for 30 minutes, and during this time, I taught my middle ds his school.
He had a Barney video time in his saucer in our bedroom upstairs. I moved a t.v. and vcr into our wardrobe and put the monitor in there. He loved this!
Scribbling in his high chair was another daily independent thing he did for 15 minutes. I taped a big white piece of paper to the high chair top and gave him markers and crayons.
In between these things, he was out playing among us, but during those times, I had my older dc working on something they didn't need me for.
For the 2-3 yo's, here's what's worked...
Still does the sturdy books in crib or toddler bed first thing in morning
Instead of "happy playpen time", he has "happy playtime" in our entryway. Yes, you heard me right, our entryway!

This was the only space left.

So, I put child protectors on the doorknobs, brought in a shelf stocked with toys just for him, and put a rug on the floor, with a blanket on the rest of the floor. I put the radio on the top of the toyshelf and put a gate up in the doorway. Through trial and error, I've figured out it's important he CAN'T see me, because then he wants me and cries at the gate. When I go around the corner to the living room, he plays very happily for about 45 minutes now, but if he sees me, POOF! That's the end of "happy" playtime. I am currently training him to do this so we can have this time to school next year (we are on break now). We will probably either school during that time in the living room or upstairs.
He still has 30 minutes of playtime with oldest big brother in the basement playroom, and he also now has 30 minutes of playtime right after that with middle big brother. He's happily played with for an hour, and I can be schooling the other 2 boys, one at a time during these times. Works great!
He still has the Barney video, but on the couch instead. I trained him to stay in the room and watch it by first having him belted in to his high chair as he watched it. Then, I let him sit on the couch for it. The first few times he ran around I put him back in the high chair, now he understands that to get to watch his Barney video, he needs to stay on the couch, and he does so very cheerfully.
Instead of scribbling in the high chair, I replaced that with "choose from the cupboard" time. It got this idea from Carrie, and it works great! I cleaned out the bottoms of several kitchen cupboards and put learning toys in there (such as puzzles, Lakeshore boxes, coloring books, etc.). During this time, he can choose 1 thing. I open the cupboard and have him pick. He then can take that thing to his little table and chair (or the living room), and play it. When he's done, we pick it up and he puts it away and may choose a new thing. This is the thing we're working on now, and he's not very good at it yet. He only plays with each thing for a tiny bit of time, but that's alright. I know he'll get better at it and more interested in each thing as I show him how to play with these things one by one. I did this with both of our older dc, and it is a wonderful thing once they are trained!
So, these are just a few of my very best lifesavers for teaching multiple dc with a crazed little one joining the scene!

Each of these things I have trained my dc to do, slowly, usually one or two at a time. We rotate our school around to not be within eyesight when toddler is doing his things on his own. I also try to rotate these things with free playtime for little toddler. These are just some ideas, but looking at the space in my house creatively, taking time to train little ones to have some specific routine ways of being independent, and making the schedule around the toddler has really helped my days go better.

I hope something here helps - and I am praying your baby settles into a schedule so you can get more sleep - that makes all of the difference in the world!
In Christ,
Julie