pain in right side under breast

It is possible, but not probable, that it hurts because of growth. Did you fall or bump it somewhere?? It isn't a cyst nor is it cancerous because they are not associated with pain, but you should still see a doctor if it
doesn't go away.

Have you been wearing a certain bra for a long period of time? Perhaps the wiring or the shape of the bra does not suit you and causes pain under your breast. Try not wearing a bra for a few days, and check for any bruising. If the pain continues, well, your doctor is your best friend.

I have been experiencing severe knot causing pain under my right hand side breast. What does it mean?