It was hard for me to hear this, so it may be for you too. I'm sure your ok. Right now I have this massive ache on my right side, turns out, it's my baby boys butt pushing out. I can feel his little bottom through my skin.
There is so many changes and fluid shifts going on in your abdomen, I'd just wait it out. If it's not gone by tomorrow, and you're truly worried, call the doc. But my guess is that its sore muscles, skin, ligaments, tendons et. al. (or a trapped gas bubble
)