Severely unhappy

I need to vent...this has been going on for a while, and its not getting any better...I dont know how to handle it anymore.

Has anyone else felt like their pregnancy is ruining their relationship? I'm a SAHM, and it's no joke when I say I do EVERYTHING for everyone in this house. I do all the shopping, cooking, cleaning, laundry...I take the kids back and forth to school, and their extra curriculars, with no days off...I help with the homework and do all the bath time and bed time routines alone. I'm exhausted and I'm constantly sick because no one will cover their mouth when they catch colds or get sick, which seems to be weekly, and don't seem to care that my immune system is in the toilet after 4 pregnancies. I have zero sex drive. Nothing gets the mood going...and it's not for lack of trying either. The problem: my husband thinks that I should be f***ing him daily, on top of everything else I have to do around here, and keeps pitching fits and threatening to "get it somewhere else" and calling me "just a roommate" when I tell him I just don't want to have sex. I'm at my wits end with this shit. No compassion for how I feel, no talk of compromise for hand stuff or whatnot, just immediate fit and threatening to cheat on me. I already feel like this pregnancy was a huge mistake and don't really want the baby as it is...and now my relationship is suffering, because of my lack of sex drive, and it's bringing out the absolute worst in my husband. I don't know what to do anymore. This happened...again...this morning, and I had to fight hard through the tears so my kids wouldn't think anything was wrong, and really had to restrain myself from throwing all the baby crap in the trash and just leaving. Has anyone else had to deal with this kind of thing? Or any other emotional issue similar to this? How did you cope?