Right calf cramping

I need some insight and help from the community. I've been working at my weight loss program since Dec. 12, and I'm still having serious cramping in my right calf. A little background, currently I'm at 295#, 42 y.o., and have been doing recumbrent bikes, light weight lifting, and a modified C25K. I'm on my 3rd try at week 3 because of this cramping problem. It usually starts around minute 10 or so. My knees feel good, not great, and I jog at about 4.8 to 5 mph. I also stretch for 10 min before I start. Could this be a problem with pronation? How do i tell? HELP!!!