Dry Spell

I don’t know what to do. My fiancé wants to have sex quite a bit and I’m just not up for it. He thinks I’m making excuses because I’m not attracted to him and I hate that but he always wants to do it when I’m exhausted or when I have a headache and sometimes I just don’t want to. He’s starting to get upset about it and I can’t tell if it’s mad because I’m supposedly making excuses or just upset because he thinks I’m not attracted to him or maybe just a mix of both. But when he gets like that he just seems so down. Last night we had sex for the first time in 4 days and I was definitely exhausted but I did feel like doing it. I don’t know what to do. Any advice?