Arms pain - as though after weigth lifting - though I did not do any such activities.

Hi I have a pain in my right arm - probably in biceps muscle that is similar to the pain people get a day after weightlifting. Except that I did not do any weightlifting / carry anything heavy exercised my arms for many days. Could anyone help to identify what I have and what to do?

It is probably a tendonitis in the shoulder, however, i would need a better history to give a definate answer.