Have you lifted anything heavy recently? Just asking as my cousin damaged a muscle after lifting some machinery on his own and had similar symptoms. However, as everyone is different I would go to your Dr to rule out anything else.
How deep in does the pain originate? Do you feel like the pain is more posteriorly? Maybe like a contracting sharp pain from you back? If you feel this on both sides and towards your back it could very well be your kidneys. I would suggest going to your PCP and getting a urine test. I had personally puked from intense kidney pain myself because I had a kidney stone.