I got a mass in my right breast, i made mammogram & dr.told me that it's mass of water coming from stress, she removed it by injection.is it sth serious.

It was probably,Cyst: Cysts in breast are common; they subside with a needle aspiration of the fluid. So keep an eye on this area and be looking for any new lumps when you check your breast , which you should do once monthly(right aftewr your menses are over/stopped, by 5-6 day of your cycle. Any breast mass requires careful evaluation by your doctor.

Cyst: Breast cysts are benign, can cause tenderness in the breasts specially before menstrual period, they can resolve on their own, or aspirated like you had done.