What's a good way to treat my sore elbow?

I accidentally jerked during a plasma donation, and now my elbow hurts (especially when I extend my arm) and is slightly swollen on the inside. I took a couple ibuprofen for the pain. No external bruising, but I think I might've damaged the tendon somewhat. I'm not sure, since I am no medical professional. If someone can give me better insight on this injury and it's treatment, that would be much appreciated.