PAIN IN CHEST WHILE BREATHING. I do now?

I had COVID in May 2021, after that I was quarantined and then I was normal till late August. But then on September I had cold and I was treated with antibiotics. After which one morning after the dosage ended I found that while breathing I get a slight pain on the left side along with pain in left hand when i forcibly inhale. But on normal breathing no pain. Then slowly the pain is constant & no sharp pain is felt. I did Chest X Ray PA View which shows no abnormalities and on ECG it shows Sinus Tachycardia and sometimes my heartbeat goes high. So what should I do now? Am I having COPD or Lung Cancer . My age is 26 & I also have quit smoking. Although I am not breathless. And I can hold my full breath for more than 1 minute and exhalation takes 15 seconds generally. Please help me. I am tensed , my hands sweat and feat too. I also think I have hyperthyroidism as I have some skin irruption that comes in my lower foot. So please doctors I need your help. I beg of you.