I am having problems becoming a vampire i am lvl 51 dark elf and im am not vampire or werewolf yet

Are you letting them use vampiric drain on you frequenlty?

i was in a battle with a very powerful vampire for 10 mins and he drained me the entire time

Well there's a 10% chance of contracting each time drain starts so if he did it continuously you prob wudnt be infctd

To become a vampire, just go to a vampire lair and fight them as long as possible till they infect you with the disease. Check your active effects menu to be sure. As for werewolf, that's a spoiler, if you want to know the answer look on UESP.