You need to get tested for STI's straight away.
You need to stop leading the second girl on, stop going around kissing her if you think she likes you as this will give her the wrong impression and lead to her getting hurt. If you aren't interested in her, then don't get intimate with her, simple as that.
Third girl, you need to get rid of. You have no interest in her at all and even though sex is great, don't risk catching something from her because she could well be sleeping with plenty other men. Stop having sex with her, if she calls, ignore it. Resist the urge to sleep with her in future. If you have to, tell her straight that you don't want to sleep with her.
With those two girls out the way, you can then focus on the first girl. You need to try and make more of an effort to get to know her, get to know her friend too, take a real interest in her. Nothing will happen if you two don't really know each other. Just make sure that if you do decide to go for this girl, that girls two and three aren't in the picture.
Oh and whatever you do, as great as it sounds to have three girls on the go, don't do it!
Good luck, I hope things work out with the girl that you like....