What Causes Pain And Lump At The Back Of Head Post Injury?

Hi, I hit the back of my head on the left side over a week ago and it still hurts. At the time, it hurt but did not swell but as the week has gone on it has become more painful and now I can feel a lump. Previous hits to my head has caused a lump straight away and the swelling reduces with time, not the other way around! Is this normal? Many thanks.