Intense pain in my arm...

[nation]

I recently started lifting with Surfinillini; I lifted for the first time in a few years yesterday.

We did back, and did many exercises, like reverse flys and other back related things.

Today, my right arm cannot extend the whole way, and my left one cannot extend more than halfway before I encounter intense pain. What should I do to alleviate the pain and get my arms straight? The pain is in the tendons between my forearm and bicep, not in my elbow but on top of it.