It turned out she was pissed that you hadn't boned in a while. It wasn't really a conscious thing, you tended to be happy to oblige, what guy wouldn't? You'd just been busy at work and tired when you got home, and the subject didn't come up. She interpreted that as if there must be something wrong with her, that you weren't interested in her recently-acquired piggish body. It wasn't surprising that she'd grown more insecure and self-conscious over it. You made a mental note to beg a bit more often.
As she climbed on top of you, still a bit miffed, you couldn't help but find her as adorable as ever. She probably felt it, too...