Constant chest pressure (left of sternum)and under left breast. Please help!!

[Marc6490]

I have been experiencing left chest pain and pressure(mostly pressure) but it is severe pressure to the point where I can't think about anything else besides the pressure. The pain seems to be in one spot on one day and another spot the next day. The spots that are affected are directly underneath my sternum in the center of the chest. To the left of my sternum and below my left breast towards the bottom of the ribs. I have gotten a bunch of cardiac tests including an echocardiogram, stress test, EKG, blood test, MRI and cat scan. All came back good. This has been going on for three months now and seems to be getting worse. The only medication I take is 30mg of oxycodone for a herniated disk. The pressure in the chest seems to get a lot worse after my dose. I don't know what else this could be. I don't think I have GERD because I don't get a burning sensation or feel like there is acid coming up. I also don't think it's constacondritis because I can't recreate the pain when pushing on the area. Someone please give me some insight on what this could be.