What would cause groin pain going from one side of tje scrotum to another?

Referred pain. Go see your primary doctor or an urgent care facility to make sure you don't have an infection.
Multiple things. Groin and/or scrotal pain could be caused by multiple problems including hernia, infection of epididymis or testicle, benign orchalgia (chronic testicle pain), musculoskeletal pain, etc. Without knowing other symptoms, it is difficult to know for sure what is causing your pain. I would advise you to be evaluated by your medical doctor.