26, Possible Lung Cancer?

Hi everyone, I'm so sorry to be a bother but I could use some advice. 

I'm 26, overweight, have always had about 85% lung function my whole life, have never smoked but both of my parents were heavy smokers for a long time. I have always been prone to infections and many, many, many bouts of bronchitis. About six years ago I had a cough that wouldn't go away for about a year, my doctor put me on a strong course of antibiotics and BOOM, the cough went away and stayed away. Last May, I came down with a mild case of pneumonia, was flat on my back for about a week. After that went away, I had a mild cough that I couldn't shake. I got sick again that Novemeber, cough came back full throttle, and I have had it ever since.

I've been to see a pulmonologist and an allergist, and they both say I have asthma and put me on a strong course of Breo Ellipta and Xyzal. I've had three chest x-rays and the first one came back with a mild positive that showed cuffing on my lungs, the other two came back clean. The blood tests for allergies came back with just a positive on dust. I will be having skin tests down next week.

The Breo and the Xyzal worked great for about six weeks and then my sister got really sick with pneumonia and of COURSE I picked up some of her ick and have been fighting off a sinus infection for the last two weeks and coughing my brains out. The cough does not come from my chest, it comes from my throat, a tickle or an itch in the back of my throat, which causes my sinuses to go nuts and activate the post nasal drip that makes me cough more. 

I highly doubt I have lung cancer because the cough is technically my only symptom and my second two chest x-rays were clean. But I wanted to run this by you guys and see what you think and see if anyone suffered symptoms like this before diagnosis. Feel free to ignore this post if you need too. Thanks everyone!