Rights of a carer

I have a 15 year old son who has Angelman Syndrome. I work full time and rely heavily on my eldest daughter to take care of him while I'm working (I best stress that my daughter is 31 and has children of her own so caring for her brother fits in with her life at the moment)  my query is about disability leave. When my son had a hospital appointment I was told that I was entitled to disability leave to take him there. As primary carer I took on the characteristics of that disability (hope this all makes sense) so was entitled to paid leave. Now im bein told i am not. Does anyone actually know the legalities of this? 
Regards 
T