risk of lung cancer at 27 years old

I have been suffering for burning chest and pain and upper back pain also feels like my lungs are burning for around a yr the 1st time doc said pleurisy and 2nd time he said i had hurt my back muscles. i do smoke around 15 -20 cigarettes ad day for around 11 years, the pain generally gets worse the further the day goes on i/e the more i smoke. bad i know (no lectures please) i have no other symptoms of cancer maybe slight fatigue but i have a job and a toddler nothing extreme and i have gained around 14 lbs in the last 8 -9 months. i have no regular ongoing cough or anything i do have night sweats but i am also taking sertraline daily for anxiety which i believe the sweats are linked to.
I am terrified of lung cancer and i know it's commonly diagnosed later in life but i have read of a few younger cases. I am intending seeing my doc again, but i am worried sick of cancer until then. i had bloods done for tiredness around 3 months ago and thyroid levels and blood count ect were all normal also had a fbc. which were all fine.
anyone please help what are my chances, please no scare stories!!!
i am female and 27 years old  what at my age is the likelyhood it is lung cancer compared with something else???
many thanks

[Dr Santos]

Hi,
How are you? Risk factors for lung cancer include smoking, exposure to secondhand smoke, exposure to radon gas, exposure to asbestos and other chemicals, family history of lung cancer, excessive alcohol use and certain lung diseases such as chronic obstructive pulmonary disease, may have an increased risk of lung cancer. This link may be helpful:
http://www.cdc.gov/cancer/lung/basic_info/risk_factors.htm
Take care and regards.