It could be stress. It could also be your diet.
And yes, it could also be the chemicals you are using on your hair. Not everyone's hair will react in that way, but yours may be doing so.
If you feel that nothing's changed so as to be a cause of your hair loss (stress, poor diet, illness, etcetera) then I would agree with you in your suspicions of the product causing the problem.
Try changing brands and see if that helps.
(I don't color my hair, but I have found that some brands of shampoo and conditioner cause my hair to break and/or fall out - it is only by process of elimination that you will discover what works for you. Good luck.)