Im 18, girl, pretty fit. but whenever i excercise/run now i feel out of breath, dizzy, a little nauseous.. i have a bit of anxiety. what should i do?

Out of breath: You may have exercise induced asthma. See your doctor who can supply you with the proper inhaler before you start exercising

May be wheezing: How long has it been since you ran on a regular basis. The problem may be exercise induced bronchospasm also known as wheezing. Need to see how you do when you run each and listen for a whistling noise in your breathing. Need to talk with your doctor for specific treatment that may help relieve it. Anxiety and nausea can accompany this.