at this point, just watch and wait. it could be just normal, it could be overactive milk letdown/ ejection reflex, it could be reflux, it could be food sensitivities, it could be a sign of something bigger like pyloric stenosis. see here for more info: http://www.kellymom.com/babyconcerns/reflux.html
make an appointment with a lactation consultant. some private ones do home visits so you don't even need to go to them. they have tons of training and know what to look for in each of the above situations and should be able to help you determine if it's something you need to get a physician involved with.
sending you hugs...