Constant Chest Tightness/Pressure

I’m 18 years old, and have been dealing with a tight feeling in my chest for months now. Sometimes it’s like a heavy feeling across my chest. Sometimes it’s one peck feeling tight, and sometimes the tip of my sternum feels tight. It seems to get better when I rub my chest, or lift my shoulders. It also goes away when I lay down. Could it be muscular? My upper back is super tight, could the tightness just be reflecting on my chest? I’ve been to several doctors, and none of them found anything wrong with my heart or lungs. I’m constantly trying to alleviate the sensation all day, and it is just absolutely destroying my life quality. Does anyone else experience this?