What's wrong with my running?

It's the second day of track and I'm not new to running. I did cross country, and it feels like running on flat surfaces is harder than cross country. ? I feel like I can't run as fast as I can like in cross country. I'm going to be a distance runner. My lungs hurt so bad that I can barely exhale. I DO NOT hyperventilate when I run. I make sure to breathe slowly, but not to slow, in rhythm to my running. I had to stop a couple times because the pain in my lungs was un-imaginable. I have never, ever stopped to walk during a run? What's going on? I ran 2 miles almost everyday a month before track. I'm not bad either. Could it be asthma or a condition related to my lungs?