Re: Throbbing pain during arousal...it's a long one
Sanda2007, you may have a pudendal nerve issue.
The pudendal nerve controls all sexual sensation, as well as the anal sphincter and what nerve endings you do have in your vagina and vulvar area. When it is inflamed, it can cause pain or numbness in the rear or buttocks, oversenstivity of the vulva, painful spasms in the vagina, heightened or painful arousal, etc. It sounds like this may be affecting you on one side of your body only, which can happen.
You should avoid caffeine in your diet and also avoid any sexual activity for the time being (including masturbation), to see if this starts to calm the nerve down. You should also try basic pelvic floor relaxation exercises, because when the nerve is acting up, it makes the muscles of your pelvic floor tense, and that just irritates the nerve even more. You may in fact have a chronic habit of tensing your pelvic floor muscles and that only aggravates the condition.
You can also tell your doctor and he may be able to prescribe something that will calm the nerve down (although these drugs tend to also kill your sex drive as long as you take them, unfortunately). If you have experienced this for three years it may take time for it to go away.