S.S.
My son was also potty trained just before turning 3, and we had a 10-month old in the house. I'm sure it's harder with a younger baby. He didn't have quite the big problems you're describing, but after the first week or so when things seemed to go great we have had some setbacks. Pooping in the potty was the first hurdle that took at least a few days (and more than a few #2 accidents in his undies, yuk!) He's had mini leaking accidents ever since he was trained, where he won't go potty himself unless he has to go REALLY bad, and already leaked, needing a pants change anyway. This has gone on for weeks now and we're not sure how to stop it. Also, we have night wettings and such, but we just take it a day at a time. Plus, he'll never go when we suggest it. It has to be his idea. We tried setting a timer, and when it goes off, it's time to go potty- that way it's the timer's fault, not mine! That works sometimes.
We've also had periods where my 3-year old seemed to be dropping his nap. Don't let him, though. Keep trying. We have had days where he will stay in his room for a short time and then come out, refusing to rest, and other days he took a 3-hour nap. It was crazy. Now, however, we're back to napping about 2 hours most days, and I'm so glad I didn't give up. You might have to try the normal naptime routine (read a story, whatever you do) and then if he leaves his room he gets the door closed on him- my son hates that, and will usually stay in his bed then so I won't close the door. Same goes for crying- door gets closed (and I have had to hold it shut sometimess). Or, try lying down with him if the baby's sleeping (try to coordinate their naps). You could also give him a stack of books or quiet toys and tell him as long as he's quiet and stays in his room he can read/play, but if he leaves then he'll be in the corner/time out chair/ get a spanking (whatever you do) as punishment. Stand strong mommy your time is worth it, and he needs the sleep as you know, and you are the parent- he shouldn't be calling the shots (but I know that's hard sometimes since we can't control their every move. But we can influence it strongly)! Our doctor's office told us to not let our 3-year old drop his nap- that kids up to kindergarten age need at least a quiet time. Best wishes!