What happens to your hair after you dye it?

As a younger teen from 15 years old (now 17) I have dyed my hair quite a lot... Before I turned 16 I had dyed my hair quite a lot.. Every two weeks I had dyed it another color. For my 16th birthday I changed it and decided to dye my hair back to brown and chop it all off my hair went from touch my waist too just below my jaw line. I needed to change and stop dying it as much as I did. At the moment I'm a bit worried because my hair doesn't grow as fast as it use to when I was dying my hair. It's just past my shoulders and I have already turned 17... My hair is falling out quite a lot, but not that bad. My mum says it has nothing to do with dying my hair but more to do with the fact that I don't eat as healthy as I need to be, like more fruit and vitamens ? What can I do to make my hair grow out healthier? How do I have nice healthy hair? HELP!