After retinal detachment surgery, is it normal for your eye to hurt months later?

Possibly. Pain can occur months later. Pain is more commonly associated with scleral buckle surgery or long term silicone oil.
It depends. It depends what kind of surgery was necessary for your retinal detachment. Scleral buckle can be a source of irritation months later, but severe pain is never normal. You must be followed by a retina specialist and ask them for their opinion based on an actual examination.