Babies can regurgitate a small amount of milk. If the weight gain is good and baby has good activity then don't worry.
If your baby has a lot of gas issues, is not gaining weight, seems hungry and irritable all the time , then you need to consult a pediatrician.
Your diet may need to be changed and baby may require testing .
Next Steps
Seek an appointment with a Pediatrician if baby has issues as mentioned above.