Chest Discomfort/Pain for 3+ Months

I'm a 28 year old male with no history of heart or lung problems. I've been dealing with mild chest discomfort for over 3 months now and am in need of some answers. This pain sits in the center of my chest. It doesn't worsen with exercise but after sleeping the pain improves dramatically. Most mornings, I do not have any chest pain until about 8-9am. I do not have any other symptoms currently. My pain has never been very debilitating, mostly it's just a irritating pang throughout the day.

I have visited a doctor 4 times trying to diagnosis the pain. In the beginning, two coworkers and I started having chest tightness and stiff joints all that the same time, so we assumed it was something viral or bacterial. None of us had any sort of cough, fever or other symptoms. The pain would escalate throughout the day, some to the point where one coworker went into the ER thinking he was having a heart attack. Initially, we all suspected Walking Pneumonia. I did a round of antibiotics (z-pack) and was beginning to feel better. But, at the end of the following week, the chest pain crept back in. This was consistent with my coworkers as well. I also took Flonase for a couple weeks.

I then suspected some sort of mold exposure since we work in a fairly old office space. Blood tests for mold exposure came back at low levels, but nothing that should cause any symptoms. The office was tested for mold and those levels were again low, but not harmful. I then had blood samples taken to test for other allergies/red flags, chest x-ray, and EKG, all which came back normal. I was prescribed an inhaler to see if that would open my airways. The inhaler did not help. I tried changing my diet to see if it was my acid reflux acting up (which I've had most of my life and take Omeprazole to control). Initially my pain seemed to be lessening, but after a week of an adjusted diet, the chest pain remained and it might have just been a placebo affect.

I don't have any other lung issues that I've noticed with this, so I'm unsure if I'm in the correct discussion group. My coworkers are still experiencing this chest pain/discomfort as well. I'm fairly certain it is not heart related since all tests came back negative. Any suggestions for what might be going on? I'm having a follow-up doctors appointment soon, but I wanted to try my luck here since my doctor has not yet been able to diagnose the pain.