Well done, you have clarified things greatly, and have just taken the first and most important steps to good health. Your smoking history makes it quite clear that there is some damage to your lungs, but you are young enough, PROVIDED you never smoke again, to look forward to eventually having a normal life expectancy.
Do not do anything else to damage your health, because a full recovery of health can take not months, but years, as you will see if you google the search term 'stop smoking benefits timetable'. There are lists of benefits by time, which start from a few hours and go up to some 15 years of continuing lowering of risks for things such as diabetes, heart disease, lung disease, stroke and cancer.
For an example from this list, take where you are now, 2 to 4 weeks, and it says 'Cessation related anger, anxiety, difficulty concentrating, impatience, insomnia, restlessness and depression have ended. If still experiencing any of these symptoms get seen and evaluated by your physician.' So you can see why you are feeling very down and stressed out at this time. It is withdrawal symptoms.
Most people say they have no problem stopping smoking, they have done it dozens of times !! An old joke I know, but you now have the ultlimate incentive to make it stick: you KNOW you have damaged your lungs.
It is hard, and may I say that some people think using e-cigs will work, but in my opinion, you are just exchanging one addiction for another one. Yes, it is hard, very hard to give up for good, but it CAN be done. Please do whatever it takes to succeed for your own sake.