Extreme Hypochondria. Lung cancer? In need of advice.

I am a 16 year old female. Right now, I believe I caught a cold from my mom, but im not sure not that I have all of these possibilities in my head. My back & ribs hurt so bad. When i cough, it sounds like a bark & my back goes in excruciating pain. I coughed up mucus & it was a little green but mostly clear. (i know too much info lmao). Bit i have extremely poor posture, like it's really bad. & i have tore something in my back before so that might be why idk. Now I just got suddenly nauseated & the first thing that came to mind was cancer. Why? I have no idea. It sounds so stupid. I'm tired of these negative thought racing through my mind. They're controlling my life. But it's hard to focus on the postive when youre symptoms are so bad. I get so worried by minor symptoms. I always believe that they are an indication of a serious health problem. People keep telling me that when i think I have a disease, i can actually cause it in the future. They keep telling me not to think about it & ignore it but trying not to think about still puts thought into it. Idk man I just need to know that I'm okay despite how horrible I feel. I've written on here plenty of times & i still don't feel reassured. It's really stressing me out which i know isn't good for your health either. It's just a cycle of bad habits, stress, & negative thinking going on & im afraid I'm going to cause a serious problem soon If i don't stop.

Sorry to ramble, thanks.

Thinking of it won’t cause it in the future, however, thinking of it may give your mind the fuel it needs to alert you of the danger and associated symptoms so you become hyper aware of these potential issues may actually cause you to feel symptoms associated with those problems. 

What are you really worried and thinking about? Your health, your family, your appearance, or all of the above? You have to narrow down what you  are thinking about.  If you have OCD thinking, you will have a lot of traffic in your head. Make some notes about what is your top priority, what you are worried about most, next, then realize that a lot of it is just worry, what do you feel about yourself?