Then you don't have DID.
Yes, it is. There is a normal spectrum of identity confusion and dissociation both - all humans have this to some degree, which isn't pathological. And then there are pathological versions which are pervasive and fixed - disorders like BPD, or SZPD, for example.
This would seem to be a direct contradiction of your first statement, though. If you don't have different parts inside of you, then you don't have other personalities inside of you, either. If there's no evidence in your life that you secretly have different personalities you don't know about, then there isn't much productivity to ruminating on it. It sounds like the rumination on this is the real issue that is causing you distress. You're thinking about something that scares you, but the actual thing you're afraid of isn't a relevant factor of your existence. By your own account, you
know you don't have other personalities.
Essentially you're afraid that you could have DID without knowing it. But this is because you have OCD. You're obsessing about the fact that you could be doing stuff that you have no memory of later (this is a form of OCD called
False Memory OCD and it's very common) and making up scenarios in your mind that could happen and ruminating on those. Treat the OCD first, because it's your most significant problem right now. The majority of your threads on this site are related to whether or not you secretly have DID, and this is a compulsion.
Compulsions don't look like washing your hands a hundred times or turning the lights on and off - most compulsions are verbal (confession, reassurance-seeking) and/or research-related. You become anxious over this possibility, and feel
compelled to reassure yourself over and over again by repetitively asking others if the factors of DID are in any way applicable to you. I would wager this is why people are starting to become less patient with you, because you're receiving the same answers over and over again, but only a short while later the anxiety you feel creates the urge to ask yet again.