Pleeeeaaase help! phlegm!?

ive had this really bad problem with phlegm since towards the end of august, when i was camping in maine. i get really bad phlegm and anything i eat or drink, it aculates in the back of my throat like phlegm. it makes me feel really sick and yucky!! ive lost some weight because i feel like i cant eat or ill feel sick. what should i do?