Possible pulled muscle
IDK (Just want to put you in the active section.)
Its more than likely a pulled muscle but still get it checked out. It may be something more, don't take the chance and injury it further. Good luck, I hope you feel better.
Get it checked out by a physician. It's probably a overstretched muscle. Best thing you can do is don't work it for awhile. And Ice It Possibly.
Because of the bruising I'd recommend consulting with an MD. If it was only pained I'd think muscle pull, but bruising could mean a tear or rupture in the muscle. Are there any soft spots or indentations in the muscle compared to the other side(another indication of a possible tear.) Good luck and ice it down.