Open Question: Slight pain immediately after workout?

im in good shape, i work out and i know better than to hit certain muscles 2 days in a row... but sometimes i get a strain in my upper arm after lifting... its not a serious pain it doesnt really effect my life but i was wondering if it is normal? its very deep in the arm...i actually got it in my leg today also. its just sort of a strange feeling. im probably too vague to get any real info