Life events can affect the chemistry in our brains. Stress can lead to depression. Unfortunately, the molecules that stimulate this response are long lived. (It's actually a protective response, but it don't feel good!) So keep plugging away at solving your life problems, and there is a good chance your chemistry will improve. But it is not overnight because those molecules last so long. Some of the studies I have read show half lives of 6 weeks for some of the stress-induced molecules that can lead to depression. Hang in there!