After & Sometimes during baby throws up milk and it is phlegm-y?

She's 4 weeks old and we have an appointment friday for her check up, i already know to tell him i think she could have acid reflux, and i'm already feeding her soy but now when i feed her and prop her up to be burped almost always milk comes back out but now it has been phlegmy, she does sound a little congested but i'm a new mom and thought i'd ask if anyone knows if this phlegmy throw-up is related to anything other than congestion/allergies?