Sorry, the only think i know, is that, you can have problems casting drain if you follower is Serana.
So what you can do actually is this: (try to become a werewolf again and after that a vampire) (maybe this will trigger something and you will again cast drain or feed !!!!)
I have found this:
DLC Dawnguard Information
If you have the DLC Dawnguard you can flip back and forth between the too.
In Dawnguard, "if you are cured of Lycanthropy or if you become a vampire lord you can talk to Aela and she can make you a Werewolf again" and it cancels out your vampirism vice versa.
"If you would like to be a Vampire Lord again, speak to Serana."
Skyrim without Dawnguard
Without the DLC once you are cured of Lycanthropy. You can not get it again, with the exception Hircine's Ring. As long as you don't have Lycanthropy, you can contract Sanguinare Vampiris (which turns you into a vampire) from a vampire.
There is a 10% chance to contract it when they cast Vampric Drain on you. If you cure it you can contract it again with the same method.
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The important thing to note is Lycanthropy cures Sanguinare Vampiris. So if you have Sanguinare Vampiris and then get Lycanthropy you will cease being a vampire.
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And something else: If you delete your DLC's you won't delete your patch.
Because the patch is in your Skyrim folder together with the main game, and your dlc's are in the Additional data folder only.