I have a lump on the left side of the back of my head and usually does not hurt but today it does if i touch it, not too intense of a pain?

Have you ever seen a doctor for that lump? It could be a sebaceous cyst or a reactive lymph node. The sebaceous cyst can get infected and it causes pain and tenderness with touch. The problem is usually resolving without treatment but sometimes it needs to be incised and drainage. A chronic reactive lymph node is usually asymptomatic.

If the lump is under the skin and not attached to the skull it could be a fatty growth (lipoma), inclusion cyst or a wen. Tenderness indicates some degree of inflammation and infection would be a concern. Have a physician examine and advise you. In the meantime you could apply warm,moist compresses.