While i was on my menstruation cycle i notice one day there was a pink mass (1.5cm x 3cm) on my sanitary pad what could it be ? after that my period stop for that day but came back the next

Blood clot?: Most likely this mass is just a blood clot that formed in your uterus and then was expelled along with menstrual blood. If you've had sexual intercourse in the past month, there's a small possibility that you had a very very early miscarriage. However, only a pathology exam could tell for sure. Consider making an appointment with your Gyno.