You shouldn't feel guilty about calling sick. You are entitled to have days off, don't let him make you feel guilty.
With my first pregnancy I was working at the time (I'm not anymore) the same thing happened to me. My boss was being a **** idiot, he kept complaining about me missing some work for antenatel classes and at the beginning when I had morning sickness.
It was really annoying me and I went and told him what I thought of him. I went and yelled him, I told him "You bastard, stop being such a moody idiot, if you have a problem with me missing work tell me to my face. What can I do, I'm pregnant for gods sake!" He didn't say much after that and stopped being so funny towards me. He couldn't do much though because I was the size of a house at the time and he think he was quite intimidated.
I wouldn't suggest you go and yell at your boss like I did but maybe go and talk to him about the problem.
Let me know how it goes, good luck
Lilly,6/ Paige,14mnths & my angel Maddy-SIDS