Shortness of breath witih Phentermine

I have been on this medication for 60 days and have lost 20 pounds....it has worked great. For the past 10 days I have had shortness of breath and heart palpitations. I have another 30 pounds to lose. Will any lasting harm be done if I continue the medication until I reach my goal or should I stop now? If I stop the medication, how long before the heart palpitations and shortness of breath go away?