Online Dating and How Every Guy Wants to Hookup

So I have been using online dating for 3 years now. With very little luck. Throughout those years I have been pushed into sex after just the FIRST date! I'll even purposely avoid talking about sex online and in person so I don't give them the wrong idea. How can I stop this trend in my dating life? If another guy does this to me I'm gonna have a break down! :(