you should always concern a physician to get a medical clearance before starting any exercise program…According to me,you are probably pushing yourself too hard… It is very important that you breath from your mouth and exhale from your nose while you are working out and I don’t no if u have a heart rate monitor or not but if not I would suggest that you should get one and if u r just starting your exercise,give your body sometime to adjust to it n try to maintain your heart rate between 75-45% heart rate that can b calculated using the equation (220-age)x0.75 and (220-age)x0.45 so whatever the two answers will be, try to maintain your heart beat between that range…