What could I take that would boost my metabolism, but not increase my heartrate?

I'm on a bunch of different medicines for different problems. One of the medicines I take is a beta blocker, so it makes it harder for me to burn calories. I was wondering, is there anything I can buy that will help me lose this extra weight. I work my *** off outside everyday. I workout, do sit ups, run for at least 30-40 minutes a day, and nothing is WORKING! I remember taking some fat burners when I was 17 years old, and I remember I lost 40-50 pounds that summer. I was in nice shape for a while. Then I stopped working out. I'm 22 now. I weight 200 pounds. I'm 5'11". I know most of the weight i've been gaining is muscle. I was thinking about stopping by the dollar store and buying some of those fat burners. Do any of you think that will help? It's like God purposes for me not to lose weight...