I have had sinus tachycardia since my teens. After many years of worry and tests, I finally decided that I could keep the heart rate down if I avoided bread, ice cream, MSG, sulfites, nitrates, and so on, with certain breads being the worst offenders. Since you are overweight, I highly recommend a high protein, high vegetable, moderate fruit, moderate fat (olive oil not mayonnaise) and no starch diet. That includes no corn, peas, and carrots. Eat plenty of leafy greens, and other vegetables, and drink lots of water. Take protein supplement shakes, or amino acids between meals. This will help cravings, and curb your appetite.
If after a few weeks, you don't feel better, then an EKG and further tests may be needed to determine the exact nature of your problem. There is also a syndrome called hyperkinetic heart syndrome that is especially prevalent in young men.
I'll be happy to advise you on the protein and amino acids. I'm a veteran and have had great success with this way of eating. However, if not, do please try everything else mentioned, especially lots of live enzyme rich vegetables.
Rapid heart rate 
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