When I went to get blood test for stds, there were 3 tubes of my blood taken, they don't need that much blood to test for HIV do they?

STD testing. Yes, it's reasonable that they obtained 3 tubes of blood sampling in order to check for std's. They may be checking for other std's in addition to hiv, which is why there was more than one tube drawn. Make sure you get the final results on all the diseases that were screened for on the blood tests. Good luck!