Since you are so young, it's less likely to be cancer, but you defiantly have something. It could be an infection. Have you been coughing up anything? If so, what color is it? Are you having any shortness of breath?

Write down all your symptoms and when they started and bring the list to the doctor. Also, write down all your questions and have him answer them. Unless he can hear something that points to a simple infection, he'll probably have to take a blood test, a chest x-ray and/or a chest CT.

Be honest with the doctor about the smoking and anything else you might be taking. He may not approve, but if you leave some important information out, he may miss something he would have caught otherwise. If you don't get any answers from your doctor, try to get into a lung specialist.

Also, I have to say it: quit smoking now. It's never going to get easier to quit. Don't you think this is enough of a wake-up call to finally put them down for good?

I agree with all of the above but just wanted to add that it is unlikely to be lung cancer if you are not coughing. I believe that is one of the first signs of the disease. Hopefully you have something less ominous.

The "water" sound may be liquid in your stomach. The stomach sits right under your left rib cage. Glad to hear you're quitting smoking. In the end, it will prolong your health, looks, and life.