left chest pain+shortness of breathing

I am 25years old. I have left chest pain and shortness of breathing. I suspected that it may be heart probelm and went to hospital for checkup.they took ECG,2D scan,blood test and treadmill stress test,everything was normal.Doctor told that it may be muscular problem because i was going to gym  at that time. still the problem is not yet cured. i am having same chest pain and breathing difficulty,please tell me will it be problem with lungs?

[lazydog]

Were you tested for thyroid disease?  This causes chest pain and shortness of breath....amongst other things such as hair shedding, headaches, heel pain and a myriad of other incidental things.  

Thyroid disease is very common in women - 1 in 4 women get this.  Get tested and get them to also test for thyroid antibodies, FT3 and FT4 as well as the standard TSH test.  Check the result for yourself as labs notoriously use the incorrect older range.  The new TSH range is 0.3-3.0.  Don't let them tell you "normal" or borderline...check for yourself.  Get copies of all your tests.  Best wishes.

...Julia