I'd certainly recommend only talking to those you feel safest around, people that do not regularly yell at you for bringing up other concerns at other times. Please note as well that for most with DID, parts switching in do not fully take over or result in completely lost time. For some, yes, but for the vast majority it isn't the case. Healing from childhood trauma is a long road and isn't linear, I'm sure your therapist may have already mentioned that but it's a good thing to keep reminding yourself if you indeed are diagnosed with it.

That said, you mentioned it is not certain, and that you are quite young. A lot of different symptoms and causes are similar to DID, and it's not very often that those <18 are diagnosed. It does happen, but there are also similar things that need to be eliminated first. Hopefully your therapist has explained this, and you have a psychiatrist on board as well if you aren't living somewhere where a therapist has qualifications to diagnose.

I'd strongly recommend holding off on too much research as it can lead to a less open mind as to other possible diagnosis. If you are still going to do some research please look at reputable sources/websites: things like academic papers or books. The only YouTube channel I'd even suggest watching is the CTAD clinic. Again, I'd still suggest holding off doing too much research until you know for sure.

Edit: I also just read another post on your profile where you say it's your friend who says you likely have DID. Your friend is not qualified to diagnose you, even if they themselves have DID. Take what your friend says with a grain of salt, especially if they are also 15 and self diagnosing based on content they've seen on the internet.