help identify leg pain from running?

its been 2 months that i've been jogging/running/dying and I made sure to go slow. Scout Runs starting at 75 walk/25 jog. Now up to 50 walk/ 50 run. Only thing is, the last couple times I went out I've had to take off my shoes and limp home, wincing all the way. About half way up my calf, on the inside, sorta next to my shin, I get this awful cramping feeling. I cant even go half a mile now days. Last time this happend, I rested for four days -till the pain went away- stretched, and heated the area. I just went out this morning, feeling in perfect condition, and half a mile later, limped my way home. I know its not a calf strain or a shin-splint, but that's all. My shoes are fine and environmentally, nothing has changed. I'm in Florida, so no hills to blame. Anyone have any experience with a similar problem, know what it is, or have advice?