Anxiety or possibly hyperthyroidism ?

Just to give a brief of my medical history: 25/m, active, no major illnesses. I have had anxiety problems in the past, particularly panic attacks. I had stomach pains two years ago that I had upper GI tests and ultrasound done which were normal. Blood tests were normal. I am on Prilosec, once a day. I have chronic acid reflux, it never goes away no matter what I have tried. I don't smoke, don't take drugs, and occasionally drink.
Recently, I had a bout of severe stomach cramps with ( no vomiting or diarrhea) that has been continuing off and on for about a week. I have been getting a rapid pulse often so much that it interferes with what I like to do most, is exercise. It is hard to imagine going for a jog when my resting hr is already 120. I feel like I am always thirsty and hungry as well as extremely flatulent.
I tried to work out yesterday and my heart started pounding after my first set of weights so bad, I freaked out and quit. I never had that problem before. I don't have any chest pain or discomfort that would seem to be cardiac related.
I went to the doctor once and he said it was the stomach flu. He did a CBC, which was normal. It has been over a week now and still I have the same symptoms, I want to get better as I am sick of this. I am going back to the doctor in a few days but I'm at a loss as to what to tell him. Any advice as to what to ask about would be a great help. Also, I have this constant feeling like my stomach is in knots. I am not under any large amount of stress and I am certainly not depressed.