Why won’t my boyfriend understand I don’t feel like sex?

Ladies I’m in need of some help, I’m currently going through a major health catastrophe where my ovaries are constantly having cyst form on them. It’s causing me to very nauseous, in pain and just depressed in general. My boyfriend is very loving and is always telling me how much he loves me etc etc. Anyways because I’m so unwell I just can’t be bothered to want to do anything sexual, I definitely put in the effort to try but I’m struggling a lot. He tells me my mouth isn’t sore but in all honesty I hate giving head. He always pulls out the card that he supports me financially and I just don’t know what I can do. I’m putting in the effort to have one night together, he still lives at his parents house so I hate having to be restricted when it comes to anything sexual. We’ve been together for 6 years now but lately it’s just been awful.

Am I being irrational to feel this way?