Thanks for your question on Health Care Magic. 
I can understand your situation and problem. 
Left sided 
chest discomfort in a smoker can be due to 
1. Heart diseases 
2. Lung disease like 
bronchitis or 
lung infection. 
3. 
Gastritis. 
So better to get done ecg and 2d echo first. 
If both are normal then no need to worry for heart diseases. 
Get done chest x ray and PFT. If these are also normal then no need to worry for lung diseases. 
Sometimes gastritis can cause similar symptoms. 
So quit smoking as soon as possible. It is not a good habit. Avoid stress and tension. Avoid hot and spicy food. Avoid junk food. Avoid large meals, instead take frequent small meals. 
Take 
proton pump inhibitor. 
You will mostly improve in 1-2 weeks. 
So don't worry, you will be alright, but first quit smoking and get done above mentioned investigations. 
Hope I have solved your query. 
Wish you good health. Thanks.