this should not be happening you should lose that kind of weight especially since your no where near being obese you might actually be exercising too much yeah it's possible. Have you been eating less or about the same since you started playing football so much? I'm 5' 10'' 165 and for the the past eight years starting from high school I've been playing football (american) then both indoor and outdoor track. In college it was just indoor and outdoor but it was pretty much a year long season. However I would have practice then lifted or sometimes go for as much as a 5 mile run then go lift. Yet my weight never went down by more then a few pounds in a day. So throughout the year I maintain the same weight.
I'm a sprinter so nothing more than 400m so faster than your average sprinter so I would say I burn I lot of calories the headaches that i got where rare but were mostly for an intense track work outs. Most of that was problem due to the fact that the facility had poor air circulation.
