Suggest Side Effects Of Phentermine Drug For Weight Loss

I am 27 years old and I have been taking phentermine for weight loss for about a month. While exercising I started to have sharp chest pains then my chest tightened up. I went to the emergecy room after having theese symptoms for a week. I had an ekg, chest x-ray, and blood work. The doctor told me I was fine and my test were normal. I also have rapid heart beat every now and then. Should I still be worried and can the medication I am taking cause me to have a heart attack? How safe is this medication?