This condition is called as olecranon bursitis
. In this condition there is accumulation of fluid under elbow skin. I would suggest you to show to a orthopaedic surgeon
and confirm this diagnosis. I would recommend following things to you.
1.Hot water fomenation
2. Aspiration of fluid from skin and steroid
3. Take Brufen
tablet for pain relief.
4. Avoid any more bumping and it will be better if you apply compression bandage there.