Firstly you have to be sure about it, know how it feels and what to do.
A psi vampire is a person or thing that lacks the ability to keep or maintain his, her, or it's own energy due to a leak in their astral or soul form. Because of this leak, they lose their energy as a faster rate than a person or thing that doesn't have a leak.
If you believe that you may be a psi vampire, then I would recommend doing a lot of reading on the subject. At the same time, keep in mind to not believe everything you read because it can be a bunch of wrong information. And don't go asking or seeking out other psi's to tell you if you are one or not. Only you yourself can know and decide the true answer. That, my friend, requires a lot of self searching and questioning.
Some of the signs and clues you can rely on in order to know that you might be a psychic vampire are: Weakness, drained feeling, or burn easily in the sunlight, others may include.
Habitual desire or "need" to be around lots of people.
Whensecluded for an enlarged period of time you tend to sleep alot or constantly feel tired.
When around others you may act hyper, playful, feel full of energy.
When around people too much you may feel a sense of "energy overburden in which you easily "hit the wall" in social situations and need to back away and be alone.
People who are around you may expirence depression, fatigue, or loss of energy. Which may also manifest as people avoiding for subconscious reasons.
If you feel this and need any help, support, guidance, or anything else then feel free to ask. :)
Good luck with your searching and readings.