Sorry to hear about your troubles. I also have a similar problem and let me just say you're not alone. It's like your subconscious is preventing you from achieving a state of happiness. Kind of like a dark cloud that constantly hovers over you. All I can say is that whenever you start getting any negative thoughts in your head, just take a deep breath, look around and realize that everything is just fine. Even though life can seem overwhelming at times, it helps to get in touch with what's really going on, take a step back and analyze why you're feeling this way.

Understand that what goes on in our heads, isn't necessarily what is going on in real life. Hanging around positive people who support you is also important. Whenever you start to feel like your getting depressed, surround yourself around people you love and interact with them as much as possible. Remaining solitary when your feeling depressed is the worst thing you can do. Going out to dinner, movies, dancing, etc.. can help keep your mind busy. This way you're not alone with your thoughts and you don't get a chance to feel depressed. Hope this helps you a little. Best of luck.