What Causes Painful Ejaculation After Masturbation?

Hi doctor im final year medical student i have baldness for last six years i have been using finasteride for couple of times but after a month two or three i quit it and again atarted but never used it for long time .but during on finasteride last times i have no side effects but this time i started agin a month ago i stasted testicular pain but for a couple of hours and usually subsides on its own .but from last four days i have painful ejaculation and groin and lower back pain after masturbation.i uusully masturbate ten to fourteen times a weak but for the first time i have this problem i have stopped taking finasteride ...what is the cause and what is remedy