If you are a vampire there should be a little "undead" or "monster" symbol thing in the bottom left beside your name I think. I heard somewhere that in order to officially become a vampire you have to drink vampire blood then feed on a person (pressing g while adjacent to some unconscious guy). About 3 days after I drank vampire blood I discovered I could "feed" then I saw the undead symbol. I ended up bleeding to death somehow though :I
Yeah, my problem is that I'm drinking vampire blood but when I'm next to unconscious people I'm not getting the option to drink from them. You said you had to wait a few days? I guess I can try that?
At the moment, in my save I'm sneaking and right next to the vampire with all his allies dead (in this room, at least, he probably has tons more patsies in other parts of the dungeon nearby), because I don't want to continue the save till after I'm safely a vampire.
EDIT:
I also noticed that when my vampire adventurer died, and then I came back with a different adventurer and drank his blood (which somehow hadn't dried up yet) I did not become a vampire. Maybe there is some chance as to which vampires are "infectious"? Or maybe vampire infection is somewhat buggy? It's my previous adventurer wasn't in the "vampire" state when he died - not sure if this matters? I drank a whole bunch of my vampire adventurer's blood, so I don't think any randomness with respect to getting the infection per drink should have mattered.
Fortunately I had some proven effective vampire blood preserved for all eternity inside a backpack...
Hmmm, is some vampires not being contagious a bug? perhaps we should report this?
Also, your comment on having blood from a confirmed-to-be-infectious vampire reminded me, that in my previous world I got infected by a vampire law-giver and due to some weirdness with this world generating differently despite the exact same seeds and parameters, is now a farmer. I can check legends as to where she is (IIRC she's a farmer or a fisherwoman or something less glamourous than a Law-Giver) and go kill her again.
UPDATE: Killed her, drank her blood, and I am now a vampire. So yes, it DOES seem that only SOME vampires are contagious. This is weird. But is it a bug?