Boyfriend not “in the mood”?!

Has anyone ever had where they have a high sex drive and your boyfriend started your relationship out that way and a few weeks in died down?! I feel so unattractive to him! He’s skinny and into fitness and I’m the opposite I don’t mind working out but it’s been awhile and I’m short so any weight looks fat on me! I’ve tried initiating and what not he says it’s not me he’s just not in the mood and he doesn’t know why he works out 6 days a week and works m-f so weekends happen to be our time and I just want to have a happy healthy sex life. Is it me? I don’t suspect cheating because we are with each other and in constant contact practically he misses me when I’m not around but it’s early on and I don’t want to rush things