How do I get rid of these bumps in the back of my head? I have been trying for over four years now. Please help!

Depends. Many things can cause lumps on the back of your head, from benign cysts and lipomas, to scary things such as cancer! you need to get them checked out as the way to remove them depends on what kind of "bumps" they are.
Acne keloidalis. You may have acne keloidalis nuchae. This is due to ingrown hair on the back of the scalp, near the neck. The condition is difficult to treat but includes steroid injections and topical antibiotics.