Well, fortunately, being in Eberron means you won't lose any of your divine abilities if you do change alignment. Still being a full caster gives you many options, no matter what the situation turns out to be.

I agree with the idea that you need to ask your GM whether he interprets all undead as being evil, or if the fact that you can still consider right and wrong means you can be whatever alignment you want... Wait, it took me until now to remember this, but Eberron doesn't have the "Always this alignment" category at all.

So, some vitally important things are covered just by the fact of being lucky about the setting you're in (be glad you're not in Ravenloft). Now you need to make sure you're not under the control of the vampire. I suggest seeing about casting Magic Circle Against Evil immediately, since it blocks mind control.

Feeding... I'm not sure about the solution.

Hah, I just thought of this: feed off your summons. Who cares what happens to summoned creatures?