Im sick...need answers please!?

So I'm a 20 yr old very active male. I'm a rugby player and lift weights regularly and do cardio. I just recently had a pretty bad sinus infection that was causing me to have a lightheaded dizzy type feeling. Its not causing me to feel off balance or hinder my walking its more of an annoyance with constant pressure. My doctor put me on Augmentin which took the sinus pressure away but i still have a very congested nose and pressure in my head and i'm still a little "spacey". I've had recent health anxiety problems (being nervous that i have tons of symptoms that i don't) . Now its been about a week and a half that ive been on the Augmentin. I still have a very stuffy nose and I thought i was good enough to go out and run. so i ran about a mile and a half and had one good cough that presented a dark green mucus with little brown specks in it. but it only cam up once and every time i cough now nothing big like that comes up its just clear phlegm. I have a bump on the back of my neck where a lymph node is supposedly located and my neck gets extremely sore. I just don't even know where to start with all of this. does anyone know how i feel or what could possibly going on. I just need an answer so i can go back to living normally.