be (flat) on your backif someone achieves something on their back, they achieve it by having sex with someone
[TahlilGaran] Dictionary of Contemporary English ▲
on your backon (your) backregularly criticizing you or trying to force you to do something.
My mom is always on my back about leaving my clothes lying around the house.Opposite of: get (someone) off (your) back. Related vocabulary: on (someone's) case, get after (someone)
[TahlilGaran] English Idioms Dictionary ▲