Pain in my upper arm?

[nvottennis]

The way I play is eastern on most shot from stomach below, and SW on high shots so I can flatten it out. Lately, I've been getting a lot of high balls when I play matchs -> More SW shots. Now I have this muscle plain along my biceps (Upper arm). Is this normal? and how do I relieve the pain?

 

[Manus Domini]

there is a health section

 

[nvottennis]

Ehh.. I thought it would fit this section more since I'm not sure whether I'm doing the SW shot correctly. The way I do it is I got From Low to high and on the follow through, back down. At the point of contact, the raquet head is facing a bit down but I dont really go through the ball as much as I brush the ball diagonally