Frustraded....tips?

I switched my almost 18 month old to a toddler bed. Hes been in one at his dad's for a couple months and I just found out I'm due with number 3 in March so figured the sooner I switch him over the better. He sleeps in it at night no problem. But he WONT NAP. I also have an almost 4 year old and it is becoming so overwhelming. I just switched him yesterday. Hes in daycare during the week and at his dads on Saturdays but I usually take that extra time while hes napping on Sundays to clean up from the hurricane him and his brother tend to be. On top of that I'm already so fatigued and irritable. This is driving me nuts! Any tips?