Heart and stents

My son had 5 drug eluting stents after blood blockages  that caused a heart attack at age 34( not from cholesterol). It has now been 13 months and the pain in the chest has persisted. On a scale of 0-10, his pain goes from a 4-8 daily and noone seems to give us an answer to why and what can be done about it.
Already had 3 caths during that attack because the first stents he had in one of the three collapsed and caused another attack and he had to have another one put in and then 3 weeks later which the cardiologist was aware of as was my son, another stent in the back of the heart was applied. But to date the chest pain won't stop. The doctor said when he did the third cath for the one in the back of the heart that the others he had done looked fine.
Son's blood pressure is below the norm, cholesterol is perfect and EKG's are good too. So what is the chest pain ongoing about?

[CCF HeartMD6]

This is clearly a difficult situation because of his history and having had so many stents already placed (with one of them already re-occluded). Obviously, if he is having ongoing chest pain, especially with exertion (typical of angina), it would warrant further evaluation with basic tests such as ECG, blood work, echocardiogram, and possibly a functional study such as a stress test. These tests, in addition, to a history and physical would indicate the need for further re-evaluation with another coronary angiogram. If these have been performed and are negative, it might be that his chest pain is from another etiology, which would need further evaluation and work-up (evaluation for causes coming from the GI system, pulmonary, musculoskeletal).