You don't need to see a doctor to move forward, you could ask your therapist to administer the SCID-D, which is a structured interview for dissociative disorders, as a starting place. That might help clarify things. However, I don't think that talking about parts and compartmentalization necessarily means he is thinking you may have DID. Internal Family Systems is a school of therapy that talks about this kind of thing a lot, and that's meant for the general population.

I think it's reasonable to put possible trauma aside for a while, and simply focus on communication with your parts. This is helpful whether you are a singleton doing therapy along the lines of Internal Family Systems, or if you are indeed someone multiple (with DID). I had a very fortunate childhood, but still had younger "parts" (in a singleton sort of way) whose feelings I dealt with accepting in therapy. If it does turn out that you have DID, you would be building relationships and one of your parts might eventually share with you what happened in your early childhood. If there are protector parts inside, they may not like that your T is trying to help you remember trauma -- they may feel like the whole reason they're there is to protect you from that, so the T becomes, in a way, kind of their enemy. So -- focusing instead on building relationships seems like a safe and helpful way to go (just my thoughts -- worth what you paid for them! ). Revealing trauma need not be the goal and I don't think you should feel like you're wasting your T's time if you're not discovering it.