[¯|_(ツ)_|¯]

Everyone's period is different, and since you are still new to your period, it's definitely normal for your period to be irregular.

I know that for me personally, my period is light for two or so days, then gets heavier for two or three days, then starts to get gradually lighter for another day or two. Right now, you are still new to your period so it's possible that this is what is causing you a bit of irregularity.

If you really have no choice but to swim, you are able to wear a tampon while you are swimming. Cassie gave you some directions on how to insert a tampon.

But, if you aren't comfortable with wearing a tampon, I think that you'll probably have to speak with your teacher about this. Not everyone likes wearing tampons, and that seems like a reasonable excuse.

If you ever have any questions about your period, though, remember it's okay to speak to someone such as a doctor or school nurse, mom, aunt, or other female figure in your life. They may be able to give you some answers.

Since your period seems to stop and come back I'd definitely carry a pad with you so you're prepared, just in case.