I think I have schizophrenia or bipolar. One minute I'm fine and then I'm in love with my best friend and go crazy and cry, but something triggers it, because normally I don't feel as if I'm in love with her, I just see her as a friend.
This is my main problem, but I also can't sleep. I just stay awake because I can't stop thinking - but when I do sleep I have very vivid dreams and I can't separate them from reality. I randomly go on meaningless trips in my car, walk for no reason at all; if I can't cry about a situation I cut myself, I talk out loud to myself and in my head I have conversations. If I'm in a room with a group of friends I just sit in the same place and keep still. What do you suggest I do, can you give me any help or advice?
From what you've shared I can't venture to guess at any diagnosis. You really need to see a professional in person to get a reliable diagnosis. Having said that, there is nothing you've mentioned that specifically sounds like Schizophrenia. Conversations in your head are one thing - hearing someone talking to you through the heating vent in your house is another matter.
Having vivid dreams that you can't separate from reality would be a concern.
Sudden dramatic changes in mood and perception can be a sign of Bipolar, but it's not the only thing that could cause those symptoms. Regardless of the reason for these experiences, it sounds like something is going on with you that needs to be addressed. Seeing a good psychotherapist that you trust would be a great place to start.
Sometimes these sorts of distorted perceptions can be a sign of psychosis - and that can be caused by many different things. You shouldn't try to figure that out on your own.