Munchkin, sounds like maybe you're not warming up properly. I find it's not good to start running straight off, even a slow jog, but give myself a good fast-walk warm up for 10 - 15 mins. At the moment I am getting back into running and using a treadmill but making use of other gym facilities before embarking on my treadmill session. I find by the time I'm ready to run I'm nicely warmed up and can start a proper run very quickly, but I'd suffer if I started from cold.