Sex life HELP !!!! WHAT'S WRONG W ME?

Okay so my husband and I HARDLY ever have sex!we've only been together for going on 3 years .. i dk if its important but there is a age gap. When we were fist dating we had sex all the time!!! Sometimes even twice or 3times at night and that's what really attracted me to him im a very sexual person so I loved that I got pregnant last year and we hardly had any sex he always had an excuse now that my child is 3months old Im on birth control we are still not having sex as much as I would like we berly have sex 1 if im lucky 2 times a week!!! I dk what to do .. it makes me moody and cranky I have literally tried everything and nothing works! ! HELP! !! ADVICE! !! PLEASE I really want to save my marriage