Fed up with no sex!

When we first met we did long distance for 6 months we lived 3 hours apart. So pretty much every weekend I would drive to him or he would drive to see me. The Sex was great, we would have sex at least 2-3 times over the weekend. Over our first Christmas together we both had 3 weeks off work and of course decided to spend the entire time together. Again, the sex was very frequent being almost everyday sometimes more than once in a day. 

Over our Christmas break we decided to move in together and a few months later I made the move to his town and got a job etc. 

After moving in together the sex very quickly became less and less frequent. (Yes I know it wasn't going to be every day forever) however I was quite shocked that within a month we were down to having sex once a week twice if I was lucky. 

Fast forward to now and we barely touch each other. We can go anywhere from a week to 8 weeks gap between having sex. Most of the time it's 2-4 weeks between each time. THIS IS NOT ENOUGH FOR ME. I have spoken to him about this at least 10 times over the last 2 years and he normally just gets his back up and tells me he has a low sex drive. I have suggested going to the doctor he says he will but never does. I feel like an absolute piece of shit that I'm not good enough for him and the last few times we have spoken about it he makes these promises to have sex more and stuff but it never happens.. 

I just would like it to be 1-3 times per week. Yesterday he made a 'promise' to have sex tomorrow, anyway last night comes and he goes straight to sleep. I'm fed up with feeling shit and I don't know how else to talk to him about it or what else to tell him because this can't continue. Any suggestions? Oh and I know 100% he is not cheating on me so please don't say that. Any other input greatly appreciated...