I feel your pain. My dd is 2.5 and in a similar space ie knows when she needs to go, can hold on forever, gets upset if I suggest using loo/potty (though she successfully did both before her little brother arrived 3 months ago). I couldn't bare feeling so stressed and obsessed about it, so have put her back in nappies. My hope is that when she is ready she'll just do it. Very hard not to despair, though.