I remember that feeling of being overwhelmed! Having two who depend on you is much more taxing than one. :) Being a SAHM is wonderful, but can be exhausting!!!
When I just needed a break after my daughter was born, my husband would keep the kids away from the bathroom door, and I would go take a 1/2 hour or hour and soak in the tub while reading a book. My son would fuss and cry that he couldn't be in the bathroom with me (he was 2), and my husband would help him find something else to do (wrestle around with daddy, read a book, put in a video, play outside, get out the trucks and push them around, etc.). I was able to tune out the crying/fussy kids for a little while because I would get into my book, and know my husband was capable of handling them.
My husband, Nate, was better at helping our son play in his room by himself for a little while (we kept a few safe toys in his room like trucks, blocks, shape sorters, Leap Pad, etc.). He would tell him he needed to play quietly in his room for a little while. Of course our son would start whining, and Nate would firmly tell him that he needed to go in his room and find something to play with, giving several suggestions. Eventually he would go, and end up entertaining himself for 15 or 20 minutes. Now he can be very independent, and we don't have to entertain him at all. We play games together and have lots of together time, but if we need to have adult time, we can tell our kids to play quietly in their rooms, and they will. We just had to help them learn how to do that.
I guess it boils down to having help. Recruit you husband to help give you a break - maybe every night after dinner - for a few minutes (even 10 minutes can give you a sense of sanity). Eventually, add time to it, like on weekends, get a two hour break with no kid responsibilities. As your son learns it's o.k. to be away from Mommy, you'll get the space you need, and he'll be better adjusted to situations like day care, church nursery, or school.
Good luck!!