My boyfriend of 2 weeks is all over me. WTF?

Okay so me and this guy have been going out for like 2 weeks. And yesterday he started touching my butt and he slapped it i was like ummm? And felt wierded out. We were all cool and stuff till he started doing being all over me and my butt and then started being nasty kinda. Idk what to say, i mean i really really like him and dont want to lose him but since he started doing that i felt uncomfortable. Btw im only 15. Hes sweet and stuff but i just wish he would stop, how do i tell him? Or not tell him but give him hints? I REALLY DONT KNO WHAT TO DO. I just want him to stop being all over me and stuff. I dont want him think he can do whatever, i have bounderies. And i dont wanna break up with him because i really like him. I liked him better when we first started going out. But now hes just kinda being preverted, not a lot, but a little. Hes not telling me to have sex or anything. Like IDK. I just want him to stop touching my butt.