Chest pain spread to back&hypochondriac.

About a month ago got symptoms like diarrhea,stomach pain, body ache,moderate chest pain, headache, fever ,rapid pulse rate with low oxygen level till 90.Got treatment for covid. Everything was okay until my chest pain started again. Get my xray done and consulted with doctor but he got to no conclusion and prescribed mentioned medications. In CBC ESR was 17. I used to smoke in the past but left it before 4 months ago. Sometimes Sputum comes out with small perticals in it and Sometimes clear white phelgum. But generally Sputum doesn't come out without taking steam. Now from last two days, again I'm having moderate chest pain Sometimes spread to the upper abdominal. What should I do and what kind of tests should I get done to know about it, why it's happening. Or what could be the possible reason for this symptom? Thanks.