Light strokes symptoms and conditions

I am a 55 year old female. I had a heart attack in July -08. I had a stent placed. Since then I have been on Plavix, Lopressor, Lisinopril and Lipitor. I have been back to the Hospital 2 times since then. The first time they found nothing. The second time I had to have another stent place because the first one didn't work. This last time they did another catheter and found nothing. I have episodes every couple days of Light headedness, heart pounding, stomach upset, confusion , really bad burping and sometimes diarrhea. I am at my wits end. I have lost 30 lbs and am weak most of the time. I was very active before all this and can't get back on my feet. When I ask about the medicines, the doctors say I don't think it's that. Someone please help!