I Think That I May Have A Groin Pull. Pain

I think that I may have a groin pull. Pain is in the upper left leg. It hurts anytime I stand up suddenly, or when I maneuver my body out of my work truck or car. Could it possibly be this or a sign of prostate problem? I'm 51 years old and the only exercise I get is working as a mailman. I'm 5'9" and I weigh 269 lbs.