My 2 month 20day boy have eye bag below his eye.

Honestly, for a baby that young, eye bags are more common than you think, it can just be genetics, and some babies are simply born with a tendency toward them. The main things to watch for are whether he is sleeping, feeding, and having normal wet and dirty diapers, because if all that is going fine, it is usually not a cause for alarm. That said, eye bags in little ones can sometimes also be linked to mild allergies or tiredness, so it is worth keeping an eye on whether it seems to get better or worse over time. Every baby is a bit different, so I would lean toward not panicking just yet, but since he is still so young, it is really best to bring it up with your PD at the next visit just to rule anything out properly.