Have a try on some natural weight loss supplement which is more healthier and effective in burning your body fat. And cardio exercise is best way to reduce your weight in a healthy way.
Fastin is the same as phentermine, which is a prescription medication that works as an appetite suppressant. Because it is a stimulant, you should talk to your doctor about whether it would be safe/appropriate for you, especially given that you are taking atenolol, which is often used to reduce the heart rate or reduce palpitations.
Generally, phentermine would not be expected to help with weight loss beyond ten pounds or so. And I expect that if you stopped the medicine, the weight would come back.
I think your current strategy is healthier and ultimately more effective in the long run - you might just need to tweak what you are eating a bit in order to start seeing things moving in the direction you like and to help with energy. And by the way, atenolol does cause fatigue in some individuals - another reason to chat with your doctor. Take care!