Could i have MPD? any help is appreciated?

i don't have any traumatic experiences, but i was alone most of my childhood, and i still am most of the time. but i don't remember very much of my childhood. and at times, i sit in the dark with a black hat and sungles on drinking black coffee for hours, and its like i'm a completely different person. when i'm like that i am very angry and a little bit twisted, and i go to great lengths to avoid all human contact. and at other times i get very depressed and i want to smoke and drink or do something else to harm myself, but i've never smoked or drank. and also i am, at times very happy and sociable. this has been going on for about a year. i've also never been to a psychiatrist, and i've never told anyone (excuse any misspellings and bad sentence structure)