diaphragm pain pain +24 year old male+

I am a 24 year old male. I exercise frequently, practice good diet and stand 6'4 and weigh 200 pounds. No history of illness or ailments. I am experiencing these sudden "bouts of pressure and rather extreme discomfort" in my chest. It seems to start from the belly button and rise, if that makes sense, almost like air filling up a space. It continues until my clavicle bone or shoulder level (top of lungs) and then goes away. This feeling does not last for long, maybe 5-8 seconds. It began after I came down with what I thought was going to be a bad round of strep/sore throat, but did not materialize. I did take some tylenol severe cold, non drousy to treat the strep, but only took 8 over 24 hours. I am concerned that it may be unstable angina, or some sort of a warning system. I also think it may be GERD, but these opinions are mine,  poorly assessed and not much credence behind them. PLEASE HELP!! Doctor visits are expensive, even with HI and these times make it even tougher...