<human>: Title pretty much explains it. In my adult life, I have always ended up drinking and hooking up with girls where there is a mutual interest on the first date (or, in many cases, we actually meet by getting drunk and hooking up.)

Right now, I am in my first situation ever where this didn't happen. We just had our third date last night, and today she messages me telling me that yes she had fun and is into me, but wanted to know if I didn't like her, or why I was so stiff and didn't talk very much.

I do like her, but I have to agree that I was stiff, awkward, and honestly couldn't think of anything to say. When messaging her, its fine. We can talk about anything. In person, though, its like my mind instantly goes blank and I can't think of anything to say. Also, she commented on my body language, just appearing uncomfortable. And again, I would have to say she is right.

What the hell do I do to get over this and make it feel less forced and more easy going and organic?

Can you summarize the given text in a few sentences?
<bot>: First time not having sex with someone right away and not getting blasted drunk with them. Have no idea how to function correctly.