You sound really stressed/depressed. I suffer from anxiety panic attacks in certain situations, but one statement really helped me through:
Depression is the unnecessary worrying over something that has already happened, it's gone, in the past, it doesn't matter in the present. And anxiety is the unnecessary worrying over things that haven't even happened yet, and might never happen at all.
How much time do you spend living in the future or the past, rather than the present?
As daft as it may sound, try meditation (actually a lot of research has been done regarding meditation in the last 10 years and it has been found that these practices do alter activity of certain brain regions). When you feel down, think of all the good things you have achieved, all the good things you have in your life. Or as I do, shift your focus to some random thing that you can see, and enhance the quality of that focus eg instead of just looking at a tree, notice individual leaves moving in the wind, the suttle changes in colour, etc.
Since this is tsr, I may get a lot of hate for this post, but it worked for me, so I hope you'll find it useful too. Looking into cognitive behavioural therapy, mindfulness based stress approaches, etc may really help you to rewire the annoying protocol that you subconciously carry out in your mind when you feel down. It certainly kept me in control when I recently went through a tough time.
Good luck
ash