I don't have any specific tips, as it's been so long since I had a toddler or three by myself all day--but I would like to say that I would try to be very gentle with YOU as you adjust. A lot of people think it's easy, even if it's something you really want, but for myself and most SAHMs that I personally know, no matter how much they liked/hated their jobs or school before, there is a bit of a grieving process involved. So if you can, try to carve out some time for self-care. It will make everything (including dealing with the kiddos) a little better. Especially since you're also going through the transition of soon to be new baby. (I'm 35 weeks pregnant, so kind of there with you in that regard, though my kids are older, 12, 11, and 11).
It's tough being so close to the end of the pregnancy and having an active child! If he's used to being active maybe you could put on some music and dance a little? Pretend to be certain animals and "dance" like them? I am not a fan of kids music but I did love Laurie Berkner and we would put on her CD a lot or dance music (I listen to a lot of electronic music). I can't remember if 22 months is too little to understand hide and seek but maybe do that? Sometimes I just gave them dry rice, dry beans and like a million containers and that occupied them for an hour. It made a mess, but it was worth it to me to keep them occupied. I also used to have a kids yoga DVD that was really cute and the kids loved doing it (as did I). I also had Kumon workbooks for tracing and cutting and stuff. They were kind of pricey for me, so I only kept them as a special activity when I was out of ideas. My daughter especially loved them. Not active, really, but interesting and fun for her. Good luck! :)
Ds loved to play catch. I would sit on the couch and gently throw stuffed animals to him. When my pile was empty, he would bring (or throw) them back and we would start over. Sometimes I did use a ball. (But he was always the ball getter...I stay on the couch.)
Can you have your dh hang a bar in a doorway? For a while we had one, and hooks in another door for a bucket.swing. and a small trampoline and a balance beam. The doorway things can be easily removed, and the balance beam can slide under or behind the couch. Anyway, my toddlers spent hours using those things.
I second the beans and rice play idea. My kids have also spent hours that way. Another idea is a small pan of water and tiny scoops and eye droppers. I strap them in their seat at the table, and put all the stuff on a bath towel.
He can also be your runner. Have him put folded clothes away, or sort dirty laundry. Or anything else.