If you have been injecting and have been clean about it then you should be ok. Its probley just the gear and your body reacting to it, and it may just be that one time that maybe you had a bad injection where you moved around little more then you should or you just hit somthing on the way.

Just take some ibuprofin and put a heat pad on the area. See if it goes away. If not then take a trip to the doctors after 2-3 more days.

If you injected other muscles on your body with the same gear and had no bad reaction then it is not a infection, its probley just you hit a spot in that muscle that reacted bad to the gear. You will be ok. Please keep up updated.