What Causes Bump On Forehead After Hitting The Head?

Hi, my son was on the dining table and decided to get up just as i turn to pour juice he basically went to sit on the arm of the chair and just fell back and ended up turning and bumped his forehead on the marble floor this happened about 7-8 weeks ago. the bump turn blackand blue and grew huge. days later it went down like 1/2 the size. since then everytime hit bumps his head he crys alot and the bump he had then still is there. now i feel he bumps his head to much and always is crying more than usual. Should I worry?