Irritated bladder

Whenever i try to go out for more than an hour or two, I stop drujba water 2-3 hours before. After i go out my bladder irritates A LOT even if I sip some water while I'm outside. A better example is when i go to school. I wake up at 8-9, drink 500-650mls before 10:15 and then I stop drinking. At 12 i head to school and at school i sip 400mls. The problem is i have a 6 hour program and with the bus and walk home 7 hours. When i get home and try to self cath it doesnr void much at all almost nothing. But i go frequently and i pee a little (naturally) a lot of times and thats the problem. Its really reallly irritated after a day of school and idk what to do. It affects my sleep, my comfort cause i wear pads everybight because the iriitation doesnt stop till in the morning.. please help