How do i tell my girlfriend im horny through body language?

Ok so ive been with this girl since july and we kissed and stuff but all of the sudden i find myself noticing things like how round her azz is and curvy her body is and stuff like this. at first i only liked her personality, the fact that she was really fun to be around, and that she was also pretty. Like i whack off and it doesnt help and makes it worse. I dont know what to do because if im just like "hey baby im really horny right now" or somethng she'll freak out and leave me. I dont know what i should do. Like i dont necessarily want to have but like a or something would be nice? she acts like she wants to all the time but then when we get intimate shes like no and sometimes wont even let me kiss her, usually thats when shes on her period though. how do i tell her how horny i am without freaking her out ? like through body language or something and what should i tell her to do about it? i know she gets this way to by the way she talks... HELP