Wow. I wish I knew the answer to that one. I really don't have any wisdom to impart, just writing to say that I have gone through something similar...impressions of things that may/may not have happened...not sure...but no actual memories. Lots of other clues, but nothing concrete.
I think these things are slippery. I think our minds really try to protect us from a lot of horrible experiences and bury them deep. That is why it always seems like we are moving through fog...or at least it feels that way for me.
How are you feeling now? Did your session with your therapist upset you or give you some feeling of relief? Do you want to do more?
I applaud your courageousness. Hang in there.