My little girl is 20 months and last week we bought a potty and just let her sit on it if she wanted to no real pressure or routine. Anyway last fri night she did a wee on it so we cheered told her well done she looked really pleased with herself. But since then she won't sit on it again and seems to get majorly stressed out whenever she needs a wee regardless of whether her nappy is on or not. I thought it could be a water infection so we have an apt at docs this afternoon but they need a urine sample apparently while shes 'mid flow' but shes so stressed out now I let her run around with no nappy on but she clings to me once she needs a wee and wees all over me in absolute hysterical cries and then points at the wet patches and says oh dear oh dear. im so worried now that ive causer this by introducing a potty or if it is a water infection I cant get a sample so will it just go undiagnosed 
please help me! !