Low Sex Drive or Unattracted?

Megan
So my husband never had a very high sex drive to begin with, but we'd still average at least twice a week. Now that I'm pregnant it's probably once a month?
At first he said it was because he doesn't want to hurt the baby. But we found out that's not possible. And now he's using the excuse that he doesn't want to hurt me because some positions will cause me pain. (I'm 21 weeks) I've told him it doesn't mean I don't want to have sex, we just can't do it in certain positions with my growing belly...
I just can't help but feel insecure (with the fact that I'm getting bigger and bigger) and thinking he just isn't physically attracted to me right now. 
Now the two choices I have, neither of which I like, is to not have sex and be frustrated or feel like I'm "forcing" him to have sex with me.