It sounds like you might be having some Illiotibial Band (ITB) issues. The ITB runs from your hip down across your knee. It's fairly common for runners to have problems. In some cases, it can be debilitating and require that a runner stop running for a while. In milder cases, stretching and foam rolling can get things squared away. You can mitigate this with some strength training (focusing on the hip, butt, and quads mostly -- I think) and cross-training (e.g., swimming).
Whatever you do, don't try to change your stride! People will generally find their natural stride, and attempts to lengthen your stride will likely result in an injury. Your stride will lengthen naturally as you get faster. I'd suggest you leave it alone and let it take care of itself.
I'll let others with more knowledge/experience correct me if I've steered you wrong. 
Don
"Don't fear moving slowly forward ... fear standing still" - Kathleen Harris
"Last is just the slowest winner." - C. Hunter Boyd