Severe pelvic pain after running. is that an std sign?

No: The severe pain from running may be caused by stress fracture. Std would be more unlikely. Get checked by your doctor and x-ray.

Not likely: Stds are caused by either bacterial or infections. They can be brought on by stress but aside from that are not really exercises associated. Also, "pelvic" pain must be differentiated from "pelvic girdle" pain. They are very different entities with a multitude of different causes. If female, first see your gyn. If all is okay there, then see a physiatrist who specializes in pelvis/biomechanics.