Why not start a gluten free diet before getting tested?

Hello. First time I've ever come across this sub-reddit. I'm very glad it exists because I have some questions for you guys and gals. I've been skimming through many articles on Celiac as when I looked at the symptoms I found I experience about 85% of whats possible. Also my half sister who was just introduced into my life has celiac an I've read that it can be inherited through a certain gene. Can't I just start a gluten free diet on my own and diagnose myself by feeling better as a result? I see a lot of warnings not to start a Gluten free diet until you've been diagnosed but have not seen an explanation on why it shouldn't be done or how it could harm me. Thank you for reading.