I totally felt that way with my first child. But I had nothing ot compare it to. In hindsight, my homroones were clearly out of control - I had horrible night sweats and I cried a lot. I thought that was how motherhood was. Of course there was some genuine emotion and a bit of being overwhelmed, but I believe my hormones really drove it. I would stay up at night holding her after a 2am feeding feeling like if I put her down I would be a bad mother. Anyway, I totally know how you feel. WIth my second child, I didn't have nearly as extreme emotions - and I even felt guilty that I didn't since she is probably MY last baby!
So I guess that I think you are experiencing normal baby blues. I don't know what to suggest to you, other than to find someone you trust who can serve as eyes and ears for you. If you fall into a true depression, you may not see it, and you need someone who is objective and strong enough to call your doctor if you can't. That may not be your husband, but maybe Mom, sister, or friend.
It will pass, but I have to say, my emotionality lasted for 9 months. I probably should have told my doctor. It might be wise for you to mention it - you don't have to take drugs or anythign you don't want to, but your doctor may be able to measure your hormone levels to see how far out of balence they are.
In the meanwhile, channel your feelings into something positive. Work on his baby book, write him a letter telling him how you feel about him, etc. But also know that the best mom for him is one who is well rested and takes a few moments for herself and for the other kids (without him). I know how strong those feelings are, so try to make soemthign positive out of them, rather than feeling sad. Good luck, enjoy him, and ask for help when you need it.