Why cant i produce babies

2 things;

1; My man has been finishing in me since May and it is now August. Im overweight but he really doesnt mind..im also pretty healthy.. Hes very skinny and healthy to an extent.. Now if i wasnt able to have kids why would my doctor put me on borth control..? I know im fertile enough to have kids and such.. But it just wont happen. My period is irregular but thats the norm for me because its been this way my whole life. So since unprotected sex isnt working i really dont know what to do..

2; i hate getting on top of my man and riding him because i feel like ill break him.. Thats how much our weight differs. How can i pleasure him without feeling insecure..