Juulie,
Sounds like you're putting way too much pressure on the whistle. I've got one Fox 40-cmg that's over 3 years old & still in good shape.
Tightly clenching muscles is a common unconscious reaction in a stressful situation, and officiating basketball in this day & age can be pretty stressful. Please don't take this as some new age mumbo jumbo - you know me better than that
- but you need to find a way to relax your jaw muscles to reduce the pressure, and to do that you need to come up with a mechanism to deal with the stress. Everyone's different & you need to find something simple that works for you. Just a hint......meditating in the middle of a game probably isn't a good choice