Tampons may seem daunting, but they might be something to consider if you don;t want to tell your teacher you can't swim because of a period. Though your period might be over tomorrow. Maybe you could get your mom to write you a note? You should not go swimming without a tampon if you are on your period still.

I find most my periods are heavy for the first 2 days, medium on the 3rd, kinda goes on the 4th or 5th, then slightly medium again on the last. It cant seem to make its mind up

Everyone's periods are slightly different, and for the first few years, you might find yours are irregular. What you've described sounds normal to me.