He wouldn't stay hard...

The last time I had sex with my fiancé, it was January 8th. Today is February 3rd. I'm currently 38 weeks pregnant.

We started having sex, and it was great for 5 minutes. Then I felt him get soft. He kept trying to go, but he was completely soft a minute later. I feel like it's because of me. I'm not attractive anymore with all of these stretch marks all over my body. This has NEVER happened in the 3 years we have been together.