my partner never wants sex anymore?

[Natalie K]

iv been with him nearly 2 years i think the main problem is im 13 years younger than him but we used to have sex 3 times a week when we 1st started seeing each other but it then decreased to once a week now im lucky if i get it once a month he had a op in january to remove a abscess from testicle so i don't know if that maybe why he doesn't want it do you think we should see the gp and ask about counselling also i feel since iv put on a load of weight due to being on mirtazapine he less interested in me should i tell him to buck his idea up or should i just accept once in while sex