How can I prevent my asthma from attacking me while I'm playing football?!

You need to figure out what triggers your asthma and avoid it. Unfortunately in your case, it seems as though it is triggered by large amounts of exercise. The problem with asthma is that it doesn't go away, and the only way to avoid attacks are to either take your medicine when you feel it coming on, or to avoid triggers altogether.
If you have asthma bad enough that you get an attack after two laps, I am amazed that they let you play. If it keeps happening, they will probably bench you. They have liability issues, and will probably require a doctor's clearance to continue.

inhaler