Your Medical Life
Things are more flexible than you might imagine but you must meet the criteria for a Class 1 medical.
Pain killers would need to be reviewed by a CAA/NATS doctor as is all ongoing medication. Depending on its precise action it need not impede your progress but, of course, you require a professional opinion.
On a rather personal note your NATS doctor will encourage you annually to be an appropriate weight especially if you are starting young as we do all tend to put it on more than lose it.
Good Luck