Periods will always start at the worst possible moment and/or when we are the least prepared for them. Always carry pads? Period will start the day after you give your last one away and forgot to restock. Going on a trip? Period will start in the car or on the plane. Beach vacation? Don't evem bother bringing that cute white bathing suit.

My period last month started when I was hiking at the top of a mountain, hours away from a bathroom. Inadequate cover to duck behind, popular enough trail that we met someone every few minutes. Fucking nightmare.

I'm sorry you had such a bad day. I hope you can laugh about it soon