C.L.
Here are a couple of ideas. You could use a bed (e.g., twin or toddler) or take 1 side off the crib (that's what we did) and then lie next to him and let him fall asleep the same way you do naps. I do this with my 2 year old daughter. We reinforced the springs on the crib with a board; since you're pregnant you may prefer to use a twin with bed rails.
You can also lay a mattress next to your bed, or put his bed in your room. When he wakes and cries you can explain that he can come find you and lie in that bed.
He probably doesn't want to be alone. My daughter loves being able to get in and out of her crib on her own- she doesn't feel so abandoned, I think. I don't mind her coming in to get me in the middle of the night- she usually sleeps about 6 hours and then comes in to our room. If it's too early, my husband will take her back to her room and lie with her.
You could also get a bigger bed for the whole family. =) This is what my husband wants to do! Lots of people have a family bed, and include everyone in the bed with the new baby.
For night time wakings, my husband took over getting her back to bed. Does your son cry with your husband? Perhaps your husband could lie next to him and help gradually get him more used to falling asleep with someone besides mommie. This took about a week or two for us for her to accept him as well as me (she still prefers me but will accept daddy and go to sleep).
I think there are some books, too, that may help- the no-cry-sleep solution and jay gordon's sleep book too.
hope this helps!