Anyone else have less sex after marriage?

My husband and I used to have sex pretty frequently, and now that we are married it's probably only once a week? His sex drive is a lot lower than it used to be he claims. It started when he started going to the gym everyday and cutting carbs almost entirely, so he was just too tired. I just am afraid that there's something wrong with me. He says he still finds me really attractive and that his sex drive is low, but I just feel so ugly. I'm only 21 and he's 23.