Having a small crisis here.. have any of you experienced something along the lines of having totally separate personalities?

This totally feeds on my lack of identity and I've been passing it off as a bad coping mechanism to deal with the mood swings that totally change my demeanor. 

I'm so lost on what to do, every me is so drastically different - It can go from mindsets, likes/dislikes, ages, some even have different names.. it's so bad I've considered there's some Dissociative disorder going on here but it's nowhere near as severe so I'm 98% positive I'm making this up and it's just the BPD..

I'm hesitant to bring this up to my therapist because I'm already so messed up I don't want to confuse her even more, and along with that I'm getting a full diagnosis next week from a psychiatrist and I am terrified I will say something completely wrong and get a false diagnosis..

If you have any idea how to go about figuring this out, please let me know..