First of all, I think you should see a proper specialist. Go back to your GP and ask him/her to refer you to a specialist, possibly a urologist.
You make it sound like you abused your body in the past and you never recovered from that. Eg, sitting all day, not exercising enough, and then overdoing it on the bike, etc.
Even if your problems were related to sedentary lifestyle, a few months of regular exercises should have solved your problems. The persistence of your problems, at least to me, indicate that they aren't related to your lifestyle.
I know a bit about the lifestyle. I don't exercise as much as I want to, but whenever I do, my sexual performance goes up a level. It definitely helps. But is it a treatment on it's own??? I somehow doubt it...
Have you considered Kegel exercises? I do a bit of those whenever I feel bored. My gf does hers as well and she's tighter than a virgin :whistle:
Another point.. what makes you think it's an infection? Wouldn't an infection heal quicker than that? I wouldn't expect an infection to last that long.