A bump in this part of the body could have several different explanations. However, the fact that it has been present for several years without much change suggest to me that the most likely explanation is some sort of cyst underneath the skin. Cysts can occur anywhere on the body and they are usually not much of a concern but, occasionally, they can become infected, and this could explain why the area is now red, swollen, and painful to the touch.
I would recommend going to see your primary care doctor
about this as soon as you can. If this does turn out to be an infected cyst (something which your doctor can confirm or rule out with a physical examination), then it may need antibiotics or even incision to drain infected material in order to heal.
In addition to this possibility, your doctor can consider other possible causes of your symptoms. These could include a boil or a large ingrown hair, although I think these are less likely given how long this has been present. Genital warts
could also cause long-standing skin-colored growths in this location, but they do not tend to become infected or painful.
Please call your doctor for help!