What is wrong with me?

I’m not sure if I even have a disorder. But lately I have been thinking that’s what this is. I tried to look my problem up earlier but I couldn’t find anything like it, except for the multiple personality disorder. I think it’s similar to a multiple personality disorder, but yet I feel that it’s different. I know how there are some people that will say they have another personality. I don’t really know how to describe it but my best way is that for example someone named Tom would have this disorder, and so the next day he would be “Bob.” I don’t know if I have that. So I’m going to try to describe what I have the best way that I can. I don’t exactly have another personality, imaginary friend etc. It’s just that, I’ve concocted another person that doesn’t exist. And I play out their life in my head, and sometimes I will play it out physically, like I’ll imagine I’m in a completely different situation. And this person and this life is the kind of person I’d want to be. I don’t do this ever in public. And I’m not sure exactly how long it has been going on but I know for sure that it has been over a year, maybe two or three. And I’m not sure what’s wrong and if this is a multiple personality disorder or not. Because I want to get help, so if you know anything about this or can help me, please do so.