Is my (26F) boyfriend (36M) not attracted to me enough because he isn’t interested in sex suspiciously often?

We have been dating only for around 4 months, but he said that he just doesn’t have much interest in sex and sometimes even when he does he can’t finish once we are at it.

I think I look fit but could it be that he is just not that into me/attracted to me physically?

How should I approach this?