I've been hooking up with this girl for about a week. Usually we just hang out and make out a bit. Whenver I try to escalate with a hand under her pants, she stops me. I'd think that she was on her period, except it's the same story when I go for her bra. She's also really ticklish, so I can't even kiss her neck without her squirming.

What confuses me is that she's definitely had boyfriends before, and I'm pretty sure she's not a virgin.

Advice?

We're both 18, by the way.