My bfs decreased sex drive

Ever since I've been getting bigger and things have been getting harder when it comes to sex it seems like my boyfriend is wayyy less interested. He still wants me to go down on him and stuff but never returns the favor or anything. He's always "too tired" whenever I want to. I'm really starting to feel like I'm unattractive to him now. I understand sex isn't the easiest thing right now but there's ways to make it work. My sex drive has increased and it's driving me crazy but I don't wanna tell him I'm mad because he won't have sex with me.