3 Year old Daughter will not potty train!!

My daughter is 3 at the end of the month and she will not use the potty!!!!
I have tried many of times, months before christmas and many times after and she just will not sit on it and have a wee. Shes a very bright clever little girl and is very good with communicating. Ive tried alsorts from her being in knickers, being bare but could not do that for long as she would scream for her nappy back on and when left in knickers she was holding on for hours dancing round wriggling with uncomfort untill she could no longer hold on and would wee on the floor. I put her back in nappies and she says 'can i wee in these now' So she knows when she needs to go she just wont be without a nappy and i felt mean leaving her in knickers as it was causing her belly ache for holding on so long and she did nothing but cry for a nappy!! I really have tried everything all the children her age are potty trained. We got her a potty toilet and she has sat on it with no nappy or knickers and she would not release her wee although she was bursting. Can anybody help and advise me as i have tried absolutely everything!!!
Thanks

[AnnieBrooke]

Be patient and don't talk to her about it any more or pressure her.  She'll do it eventually.  In the meantime, leave her in diapers or pullups, she really can harm herself by trying to hold it (especially poop).  When she sees that all her friends are in underwear, she will decide on her own to go to the potty.

[Heatherm4]

Maybe you could use incentives to try? Like having a sticker board, so every time she goes she gets to put a pretty sticker on it. Or, I have a friend that gives her daughter m+m's every time she will pee or poo. She gets 1 for pee and 2 for poo. I've also heard of getting stamps on their hands as well.
You could also buy her some undies that she really loves and have her wear them over her diaper and let her know that when she's ready to use the potty then she can wear them all on their own.