i have bipolar disorder and this is what life was like for me before i got help for it. i think people cannot really relate unless they have it. i would feel really aggravated and angry for no reason at all which could last anywhere from a day to a few weeks at a time. other times i would feel completely worthless and depressed and not really wanting to get out of bed or do anything which could also last just a day or for weeks at a time. other times i would feel fine for days or weeks at a time. occasionally my moods would change within hours, for no reason. it is not like how most people live, where an outside stimulus changes the mood, such as seeing a girlfriend and missing them or what not, it is a mood that just comes out of nowhere for no reason with no trigger and the mood is very powerful. mmoods that are actually triggered by something seem completely out of proportion with the trigger. someone turning on the TV would make me feel like i wanted to kill them. a sad song or moment in a movie would wipe me out for a week. people think you are just being moody or dramatic and you feel bad, like it is your fault and you should be able to control how you feel but you can't. actually, you just have a biological problem in your brain which is easily fixed by medication.
http://www.nimh.nih.gov/publicat/bipolar.cfm
at any rate going on medication changed my whole life-- i recommend at least going to a psychiatrist and talking about what you are going through. right now the hardest part for me is convincing myself to keep taking the medication because i can convince myself i do not have bipolar disorder when i am on the medication because i feel so much better. maybe you don't have it, but it sounds like might. worst case is you go and at least talk to someone about what you are going through and maybe feel better about what has been happening. you don't have to live your life the way you have been living it.