Suggest Treatment For Baby Having Excessive Mucus In Throat

My 6 month old daughter as been vomiting and coughing up clear mucus for the past 3 months. She has never had a fever but after every feeding she vomits the mucus, at times she doesn t want to eat because she has so much mucus in her throat. I have been to multiple doctors but have yet received a valid diagnosis. My husband and I changed her formula got rid of our dogs we are not sure if she has bad allergies. please help.