Mucus In Throat

I like playing basketball, but there was a problem that was hindering me when I play. Whenever I play, I begin to feel a sense gag and I constantly have to spit down the court on your orders. Normally, I feel like there are things in my throat, I feel just below the top of my sternum, clavicles, which are attached. Whenever I play, it feels like this stuff clogs my respiratory system. In detail, each time I play, this blockage also causes a gag / nausea feeling here. I begin to salivate excessively, the mucus from my nasal sinuses down in my throat that I force into my mouth and spit out excess saliva. Overall in this process, I feel horrible. It becomes a real problem because I am constantly out of the game and spit, and while playing, I can not work because of the feeling of nausea. I sought answers to my coaches, doctors, etc., but none of them can give me a full explanation and none of them can fix it. Does anyone have an idea of what it is? Someone else has the same symptoms? nobody knows how to fix it?

I get when I'm sick. I do not play well because of this, but I'm improving. Why do you get there so much mucus? If you can find the cause, you can eliminate the problem.