Why do I feel sick after a run?

A week ago I was running up a flight of stairs for my freshman team sports class, and I felt sick afterwards. I still feel sick four days afterwards. Usually the sickness is not that long, but yeah. I always feel like throwing up afterwards, so why do I feel that?

If your muscles are sore, that's normal. If you feel tired and nausea days after exercise, you need to explain what's going on to a doctor.