if there's not blood when you wipe, then you're not on your period.
if there is blood, then you are on your period.
stomach aches don't necessarily mean you're on your period. you could just have an upset stomach.
if you are on your period, and you want to swim tomorrow, use a tampon.
MAKE SURE you read directions on how to insert it CAREFULLY.
it will take some time your first time, so maybe practice or something?
always make sure your inserting it at an angle. it may hurt the first time, but after that, it doesn't hurt. trust me. good luck!
but you may wanna take some advil and drink some water for your nausea and stomach ache.
also, don't worry about it being late. i was the last girl in my grade to get my period.
if your mom is the type who will freak out about you wearing a tampon, just don't tell her until after you wear it. i had to wear one for a dance performance, and i told my mom 3 days later. she freaked out a lot (because according to her, you lose your virginity when you wear a tampon), so my sister told her to calm down, and said that wearing a tampon doesn't no longer make you a virgin, and if my mom asked her gynecologist, she'd look stupid.
good luckkkk.
also, if you have an older sister or friend who wears tampons, maybe call them if you're having trouble while inserting it.
i had to call my sister and my best friend and they both helped a lot.