Been drinking sour milk by accident in coffee now I feel like **** inside what should I do?
Stop drinking it and the symptoms will pass. If you feel you can't deal with it on your own, speak to a doctor who can prescribe the best course of action (though chances are, they can't do much). It sounds like you have a mild case of food poisoning. Why do you have penicillin in the cupboard? Any prescribed antibiotics should be taken for the whole course, until everything prescribed is gone. You should never have 'left over' antibiotics. They also expire so I wouldn't take anything you have 'laying around'. Ever.
sour milk is NOT dangerous. It just tastes awful. If the milk doesn't stink, or isn't clumpy, its NOT soured/spoiled. no doctor in his right mind is going to give you antibiotics for a non-existent ailment. AND no, it won't make your groin hurt.
Just take the medicine. May you be so well right now.