Been coughing for 3-4 weeks, but worse @ night times, had meds but not working. now when i cough i get sharp paints under my left breast and it hurts.

Exam: Get examined ASAP!- 3-4 weeks is simply too long and you may have inflammed your chest wall or pleural sac. You should get an xray and another opinion.

Stop smoking: While this is not likely due to your smoking, it should serve as a warning to you. This sounds like post nasal drip which can be relieved with decongestants (Sudafed) or nasal sprays. A cough that lasts more than a more should be evaluated by a physician since there are many other causes including asthma and acid reflux, not to speak of infections and other serious lung disorders. Take care.