My Baby is sick Help !?

OK so my son is 2 months old and has had bad congestion and coughing for about a month now i realized today that it was when i started him from similac to enfimil. I have taken him to the doctors once a week cause they want to see if he is getting any better first they thought he had bronchitis then maybe RSV but he never had a fever and never had trouble eating that's why they couldn't tell what it was. His symptoms are ,,,, sounds very congested in his chest. blows lots of bubbles he is only 2 months old he shouldn't be doing this yet, quit a bit of spit up here and there, and its not diarrhea but its not paste. can he have an allergy to enfimil ? I don't think its a milk allergy or he would of been doing the same thing when he was on similac or maybe its just a coincidence. I'm changing his formula today and giving it a week to see what happens but Ive never heard of allergies causing chest congestion just nasal congestion. Has anyone had this problem before ?