If the pain has been present for three years and hurts during intercourse have you seen your gynecologist at all? That would be the first step- why have you been ignoring a pain that severe for so long? You said your pain is next to your hip, if you mean inward towards your pelvis then it's probably an ovary, or your uterus. When you sneeze or cough a lot do you get a sharp pain in that area? After intercourse does it feel like it's a numbing throbbing pain? Like you have a headache feeling in that spot:?
Pain during intercourse can mean an std- if you have had it for 3 years then I doubt it's that because you would have smelly discharge, or obvious signs of an std. Sounds to me like you could have endometreosis. Look it up online and see if it matches all of your symptoms. If you have been feeling this way for three years I would go to your gyno asap. If it is endometreosis the sooner you detect it the better.
I wish you luck- hope this helps
" its been happening for over 3 years" Have you gone to your doctor? I think you should!!