Mommies, hi! Such a question, who had such that the child couldn't take…

Mommies, hi! Such a question, who had such that the child couldn't take blood from the vein? The vein is found, as doctors say, and blood doesn't go at all! And we need so much blood to be taken, there are many tests and everything is still nowhere!! I drank before that as much as possible, two times tried, already gave the mixture, but it didn't work out ? can it be like stress?