The me that I am not

I have been sleepless, tired and drained ever since the question of what or who really defines a “me” popped in my head. I get so tangled up in my line of thought that it becomes a complex ride of knots and I am on the front seat witnessing every drop and dent. I am a me that has no definition. I am a me that constantly changes. So is there a core, in depth me? If there was it would be constant, never changing, steady. But, as soon as one circumstance changes in life the “me” changes. Yes at parts I remain the same and maybe at the parts where I do remain the same are the parts that complete the core-me. However, there is a possible situation that can change even those parts of me. A death of a close one, a traumatic experience or even a change of people that I surround myself with. So is there really an in depth, core- me? Or am I a bunch of circumstances, moments, and time put together. Am I just a time with an expiration date? Born an empty vase, filled later on with circumstances that make me, me? And if so, does that mean that my existence could be the same with someone else's if the circumstances were made the same? Could a me exist twice in one lifespan but only with a few changes?

I find that it's easier to define a “me” with the me that I am not. So I am everything I am not instead of I am everything I am.