What is wrong with me?

You only feel normal at times because you've been thinking this way for so long. I can assure that it's not. These are things that need to be discussed with a mental health professional. You may have a chemical or hormonal imbalance, you could have a mood disorder such as bipolar or schizophrenia, or any of a number of things. You do need help though so you don't feel this way. Drugs and talk therapy can go a long way towards making you feel better.