My (f20) boyfriend (m21) smells down there, what do I do?

I have been with my current boyfriend for a little over three years we started dating in the summertime, which is a key detail, I swear. We pretty much got intimate pretty quickly and because I didn’t want my parents to know about our relationship for a little bit, We did have sex in his car or when we were doing anything like sexual, it was in his car so.. a lot of sweat. my boyfriend always smells great like he always smells good (cologne wise) when we first started dating despite us sweating and despite like the heat just being crazy (Arizona heat!!!!! ) neither of us smelled bad in either areas. I made sure to drink water and take care of myself down there and .. me myself I never noticed or I never thought that I smelled bad I always had that in check no matter what, he didn’t smell bad either when i first started dating him and you know all that crazy stuff and there was never a bad smell to the point where I was gagging before I even put his penis in my mouth, but for the past four months , I noticed that it’s just smelled lately and it’s not like a little smell that I can ignore and just like do my business around and avoid because I’m sure sometimes I probably smell a little off down there you know if I don’t eat right for like a day or two and my PH balance is probably a little off, but. I don’t think you guys understand what I’m dealing with. It smells so bad that sometimes when I put my head on his lap, I can’t even enjoy it. It’s very strong fish odor, which …. I didn’t even know that guys Can smell like that down there, since I’m not very experienced, but, it is so fucking bad. Like sometimes I try and make up excuses just to not give him head or to not give him like a hand job because afterwards my hands stink so bad and I love him so much like I don’t wanna tell him anything to his face, but what could be causing this? He sweats a lot and sweats really easily like I noticed that we lay together. He just gets so sweaty so quickly and it could be the sweat but I don’t think that genetalia sweat smells like fish? I just really wanna be able to enjoy sexual activities with him without getting grossed out or gagging before it’s even in my mouth or just holding my breath and avoiding putting it in my mouth for a good five minutes so can somebody please help me and explain why this is andif there is anyway that I could help him with this??