What the hell is wrong with me?

Before I start, let me just clear up that this is NOT normal. I have these random mood swings that last anywhere from a few minutes to a few days. In the sad/angry swing, I often say things I don't really mean and get mad for almost no reason, like for example one of my few freinds (few partly because I choose to only have a few) was helping a person who I don't get along with and I said "If you like him so much why don't you get a room bro". These bad mood swings cause me not to get along well with friends and family. Also, I spend most of the weekend in my room with the blinds down either writing stories or online and rarely do anything else. I'm also very paranoid over things I know I shouldn't be paranoid over. What's wrong with me? Any advice please?