Blood tests

Hello so I have to do some blood tests. Long story short, I went to go take my blood tests, and the phlebotomists say they are having trouble finding blood vessels. They said my blood veins were to tiny to prick and to get anything out from. So honestly what do it do? Has this happened to any other cf person before? Thank you. P.s. I drink about one bottle of water a day also go to the restroom at least once a day, so idk if that means I'm dehydrated or if I'm fine. 🤷🏻‍♀️ Any advice is appreciated. Thank you. (I'm sorry for the TMI.)