That is too bad that you have to go through that. It sucks to not feel good, but to have a friend for a boss is rough.
I'm not defending your boss, but a lot of women milk the pregnancy thing. Granted we do feel like we got run over by a truck a lot, but some women use that card for everything, and I'm sure from a bosses perspective it gets old. Plus he may not understand how you feel, or he's just a jerk. My former boss had zero tolerance when her staff called out, but she would call out for anything.
Are you planning to return to the same place after you deliver? Your boss is probably not going to be really tolerant when you are not able to work because of a sick baby.
Good luck and I hope the next 15 weeks get easier