What Causes Severe Pain In The Mid Abdomen?

Yesterday I started my period. White sitting I started having discomfort in my left side (mid-abdomen, toward the front) which gradually became an intense pain. I went home to lie down, intent to visit the ER if the pain got any worse or didn't stop within an hour (it had been about 30 minutes total). When I lay down, the pain dissipated and hasn't returned. However, today I'm having some sharp, stabbing pains in my urethra, enough to wake me. There isn't any burning when I pee, just a stabbing/stinging sensation every so often. I've considered everything from kidney stones to muscle spasms.

I'm 30 yrs old, never pregnant, 260lbs @ 5'5" tall. I suffer from panic attacks and anxiety disorder due to a previous misdiagnosis of intracranial hypertension and a bad reaction to Topamax. Neurologist now thinks I possible occipital neuralgia coupled with migraines and TMJ. I had taken cyclobenzaprine the night prior to the intense side pain under doctor's orders to treat the TMJ.