feelings/lack of them, in massive need of help

So I'm 22 and haven't been in a proper relationship in over 5 years. In December I met this girl and instantly knew that I wanted to get to know her, so we started talking and I got her number, I thought I really liked her. Since then we've been texting daily and have been out once-twice a week. I think she's incredible; she's beautiful, she's insanely smart and we get along so well. At the end of our second date we could both tell that we liked each other and kissed for the first time (it was a lot more than just a peck), but I just didnt feel anything. She was a great kisser and I enjoyed it in that sense but I didn't get 'butterflies' or feel anything like that, and I just couldn't understand it. I tried to blame it on the fact that I was pretty drunk, but for the next couple of days I couldn't stop thinking about it and thought something must be wrong with me. I also thought that maybe because I haven't been in a relationship for so long that I've just forgotten what I'm meant to feel/not feel.
So I went along with my being drunk theory and thought I'd keep seeing her because everything else was so good. We've obviously kissed a lot more since then and while I've come to enjoy it more, I feel that it may just be because of the absence of the surprised feeling I felt when I didn't feel anything the first time we kissed, and also knowing that she enjoys it so I do it for her sake. Everything else is still really good - we can talk about so much and make each other laugh and she seems to really like me, and while I feel that I really like her too I can't escape the feelings/thoughts that something is wrong because I don't feel this 'spark' or 'butterflies' kind of thing. I'm thinking that maybe I just really like her as a friend, but then if that was the case would I want to kiss her at all? I want to be more than friends because in my head I feel like she's amazing. The more I think about it, the more I realise that I was probably like this in my past relationships, and am thinking that maybe I'm asexual, but then I definitely felt attracted to her when we first met so I'm just so confused.
I think basically the reason I'm posting this here is to see if anyone else has ever felt this way? Maybe it's mainly girls that feel the butterflies thing, so are there any guys here that understand what I'm talking about? Maybe I'm just incapable of feeling butterflies which is making me think I don't like her, but I feel that I really should like her. I'm so afraid of letting the relationship develop and her having stronger feelings for me while I'm still feeling like this as I really don't want to hurt her.

Guys feel butterflies too, so if you're not feeling anything special then maybe you just don't feel that way about her? It's certainly happened to me before, where I think I have really strong feelings for a girl until we get physical. And then once that happens and the build-up and excitement is over the relationship doesn't seem that exciting anymore. It sounds horrible but sometimes these things just happen.

I would really think long and hard about this and decide what it is you feel for this girl. Because if you don't see this girl as a girlfriend you need to end it sooner rather than later to spare her feelings.

Thanks for your help.
It's just that thinking about it, I can't really remember ever having butterflies before. And it's weird because I really want to like her, she makes me smile and laugh and I feel like I could never get anyone as great as her again, so in a way I don't want to end things with her. I mean, what does it mean to 'like' someone - is it a combination of thinking they're beautiful as well as enjoying their personality, or is there more to it than that? I think about her a lot, when we first met I was always thinking of how I could talk to her and what I would say, and how I would ask for her number. Still I think about her most of the time but lately its just thinking about and trying to figure out my feelings for her and this situation that I'm finding myself in.

Why do you need butterflies?? There just infatuation, nervous tension and anxiety.. it doesn't mean something is wrong coz you don't have them.. i don't think i have ever had them for anyone... are you attracted to her? Does the thought of being with her sexually turn you on? If yes everything is fine.. no need for butterflies

Thanks Michelle, that's more like the kind of reply I want to hear.
I'm pretty sure I'm attracted to her - I think she's gorgeous and I do want to be with her sexually, it's just that when we kiss it just feels like kissing, I don't get any other sort of feelings and I'm thinking maybe this means I don't like her in the way I want to.

Sounds to me like your over-thinking things. When you said you weren't feeling any "butterflies" I took that to mean you weren't really feeling an attraction to her. If you're attracted to her and you enjoy her company then yeah, I would say everything is fine. It takes a while to develop really strong feelings for someone, so at this point in the relationship I;d say what you're feeling for this girl is normal.