Like really odd.

So first of all, I am your average 14 year old, going through the phases

I am interested in girls, a lot. Like, a looooooot. So, I've known this girl, since 1st grade. (I'm going into 9th.) And she knows me, very clearly. And we talk sometimes, but when 6th came (first year of middle school) I started to like her, and take more interest into her. But we also stopped talking, her mom and my mom were close friends, so she usually stayed in the same schools as I. Then, this year (which is now over) came... 8th grade. So she hit puberty, and I paid a lot more attention, but then these "odd" feelings came in, and I don't know what to do.

1: I can't stop thinking about her, she's always on my mind and sometimes I can't sleep because I am thinking about her so much.

THIS CAN BE A BIT DISTURBING
2: She's on my mind when I "do my thing."

3: I don't find any other woman interesting anymore, besides her. Don't find anyone pretty, besides her.

4: When I am around her, I get very nervous, and make excuses to get away.

I have asked her out, twice now, and both answers were no, but I said it all shy-like, and 2nd time had my friend ask. I want to ask her again this Summer, but in a way she would say yes.

Please, any help? I don't want to do, say, or even think when I decide to ask, any ideas?

I don't want to do, say, or even think

I mean I don't know what to do, say or even think.

First of all, you are not alone. Millions (maybe a billion?) of boys in their teens have intense crushes, and double that number are thinking about sex, just any sex. It's your hormones, and nature hasn't caught up with society. Nature says you are now an adult man, ready to hunt tigers and find a mate. Of course for all of history, we didn't live past about 35 until now.
Now - what to do? There's only 3 things you can do. One is to keep busy with school, friends, family, and interests. Two is to be friendly and try to act naturally and nice to her. Three is to WAIT.
OK, she said no to going out. Don't ever get someone else to ask a girl out again - any girl will be offended. Facing rejection is part of life, and this is one way we learn. Try a slightly more humorous approach - see if you can say 'I will keep asking and hoping until I am an old man in a nursing home' or something, anything, that lets her know you aren't giving up but respect her wishes to not go out.
As for tongue-tied shyness, that's common too. There's not a lot of advice for that other than to say it will go away over time.