I am a temporary SAHM (I've been on leave since 12/10/09 and go back at the end of August) and boy do I ever know how you feel! I have an 8 month old and a 3 1/2 year old and there are days where I just want to scream "I'm tired of CHILDREN!" because it feels like they're up my butt 24-7!
I know this isn't much consolation but just hang in there! How you feel is really normal even if it is grating on your last nerves - I think all parents go through this. If you can, however, tell your husband/spouse/partner that you need some 'me time' this evening and go do something by yourself that you find fun, relaxing, calming, and just for you (trip to Starbucks with a book/magazine, go get a manicure or pedicure, go to the mall, etc.)
Hope your kids give you some peace and quiet for a while. If all else fails, tuck this away and remember that payback's a b----, and you can turn the tables on them when they're teenagers and won't drag their sorry butts outta bed before noon!