Would be unusual
If you have a healthy supply of breast milk and baby is growing fast, it may seems that way.
So, when baby is hungry, feed him/her..When he/she stops sucking, then stop. Regular follow-up with doc will help guide you how to ensure proper growth and development of your precious one. It is unusual to over feed a breastfed baby. Bottle-feed is a different story, as it is easy.
Congrats and good luck.