Why do I feel like a completely different person depending on which friend group I'm with?

Like I act different, talk different, even my sense of humor changes. With my college friends I'm loud and sarcastic, with my work friends I'm calm and kind of reserved, with my family I turn into a completely different version of myself that I dont even fully recognize.

I brought this up once and my friend said "thats just called being adaptable" but it doesnt feel like that. It feels more like I dont actually have a core personality and im just mirroring whoever im around. And when I cant figure out which version of myself to be, like when different groups mix, I just go quiet and start playing on my phone to avoid the whole thing.