Frustrated and Upset with Myself!

I just got done taking a stress test for a class. I had to do at least nine minutes on the treadmill, with the treadmill inclining every three minutes. My legs are hurting sooo bad. I felt so dizzy afterwards. The sad thing is, I was suppose to go for 13 minutes so that I could pass my mile and a half. Well, I didn't do it. I love that I finally have the grades to graduate now am having the physical aspect in my way. I feel like every time I get ahead I get further behind. It's bad enough that I have been trying to graduate for the last 9 years, but now a simple thing for some is the hardest thing for me to do. Right now is one of those times that I just want to quit. Is it too late to change my major again? If I had the grades from the beginning I could have been a doctor by now, but no am going to be a teacher. Don't take it the wrong way because I want to be a teacher. However, I am not going to make that much money yet am going to be paying off school loans for 40 years to be a teacher. If I even make it to there. :( Grrrr I am so frustrated. I only thought I was at the end, WRONG!