Ahhh damaged hair

Nj
I get my hair coloured professionally (blonde) and have done for around 4/5 years. They said when started going my hair was in such good condition. Now I'm freaking out. Starting to get problems, can't use normal shampoo any more cos it itches so bad :-( and When i brush it gets all knotted and pulls loads of hair out, and breaks. The bits that come out are like short broken bits and knots of hair. I've got some anti breakage leave in conditioner and an oil one that also protects, which seemed to be working as when I last went back they said its in better condition or were they just saying that? I don't know. But I just washed my hair tonight and brushed through and it seems quite bad. I do use a lot of heat but also use heat protectors. Has anyone else has this? Maybe I should go back to my natural colour. It's just cost a lot of time and money to be this colour. Any advice would be much appreciated 
Thanks