If you are eating 5000-6000 calories a day, and not gaining weight, then I would see a doctor.

Or check your math.

I ride a road bike most days, and east about 3,000 calories a day, and my weight is stable. It's hard to imagine eating 6,000 calories in a day. The guys who ride the Tour de France do that....with double plates of pasta for all meals.

But they are using up those calories. It doesn't sound like you are doing that.