Fracture or simple bruise?! Arm(humerus) injury. Mild pain when moved.?

Yesterday I fell and hit my upper arm (elbow area) on the corner of a chair rather hard. The pain was mild and went away after about 10-15 mins. It does not hurt. The problem comes when I try to move it a certain way. I can't straighten it out completely and can't twist it in a normal fashion. There is a slight bump near the elbow and a small minor looking bruise. After a day of moving it a bit, it now hurts when left still. Not significant pain, it's a little achy at the bump and around it when moved or touched (too hard).

At first I figured it was just a bruise and went to bed. This morning it still hurt and I still could not move it properly. I told my mum and she doesn't think it's serious. She thinks the mild pain means it's not serious but I don't always respond to pain in the right way. It could be more serious and I'm not registering the pain correctly (i have some issues with hyper/hypo-sensitivity that she doesn't know about).

Should I go to the ER? Or call a doctor?