Is my boyfriend cheating on me or is he just old?

My boyfriend is 12 years older than me and I’m seven months pregnant with his child. We’ve only been dating a year but up until recently, we would have sex like 4-5 times a day and it’s always good. He would always beg for it (We don’t live together) and it would be on his mind all the time, which worked perfectly for me because I wanted it just as much as he did.
Lately, I’ve been the one asking for sex (which I’ve never done) and sometimes he turns me down (which is very unlike him). And when we do have sex, it’s only once or twice A WEEK. This has been going on for a month. I brought it up twice, trying to figure out what the issue is, but he always says there isn’t an issue or ‘idk’. Everything else about our relationship is the same, except that but I’m starting to think there’s someone else. I don’t want to tell him I think he’s cheating and seem crazy.
What do you guys think it could be? What should I do? I’ve brought it up twice, and I don’t want to be annoying but it’s bothering me
Is my boyfriend cheating on me or is he just old?
Post Opinion