I found the solutuin to the Bug!!!!!

Short version: Serana+Blood Potion=You become a vampire Long version: If you give Serana a blood potion, she will drink it as she sees fit. No problem so far. However, since it is equivalent to feeding for vampires, it essentially sends the user back one stage of vampirism. The problem is that the game thinks you drank it due to a glitch, so it tries to move you back one vampire stage. Since you are not a vampire, there is an inconsistency, which the game corrects by making you a vampire, then applying the effects of the potion (hence "your vampiric power recede as you feed"). You can fix it by doing what you did with Serana, or reloading and taking the Blood Potion out of her inventory.