I have overian cyst its 5 cm. can that be painful. my doctor said no?

Certainly can.: A five centimeter ovarian cyst is well within the range of what is considered normal - many women form cysts this size and have no pain. However, a cyst this size could cause severe pain if formed rapidly by filling with blood - usually this is treated with pain meds, but could require surgery. It would cause severe pain and would require surgery if it is twisted (torsed ovary) around inside.