I'm getting touched daily at school

I'm 16 and i'm a pretty skinny guy. And one of my female friends started poking my hips a few months ago. We would laugh about it, we're close and i didn't really mind that much. Then about a month or 2 ago one of my classmates started to come up right behind a start squeezing my hips with force. She now does it every second or third day. And everytime i tell her to stop, she doesn't. And about yesterday my now closest friends started to poke my waist, but like way more often than the first 2. I know i'm probably overreacting, but i just feel so much like a man slut and im crying on school toilet. I have no idea how to tell them to stop with still being friends with them.