One of the diagnostic criteria for DID (at least in the DSM-IV; I can't remember for sure if it's in the DSM-V) is amnesia between alters, so it's not at all unusual for people with DID to have memory loss like you're describing. Of course, there are also other things that can cause lost time, and we can't diagnose you.

No one can really force alters to come out, and even if they could, that would probably be counter-productive in that it's profoundly disrespectful to those parts. But there are diagnostic tests that can be done to diagnose DID--the Dissociative Experiences Scale (DES) and the Structured Clinical Interview for Dissociative Disorders (SCID-D) were the two used when I was diagnosed.