I understand that depression can be a symptom of low testosterone and I read that low testosterone may contribute to low serotonin levels. It's that chicken or the egg thing again on what came first: low serotonin or low testosterone.
So the question is what do you try to treat first?
A pragmatic approach would probably be to see which type of hypogonadism you have relative to how old you are. If you have secondary hypogonadism, meaning low LH and/or FSH levels, and you're under forty or so, then something's going on to suppress LH/FSH and possibly GnRH which stimulates these two hormones. Chronic stress would be a huge umbrella of possibilities for suppression of these hormones, and could range from a chronic infection to poor thyroid functioning (which involves high norepinephrine, etc.), insulin resistance/diabetes, or chronic psychological stress. Neuroendocrinologist Robert Sapolsky says that during surgery, the moment an incision is made GnRH/LH/FSH drop to close to zero -- all from such a seemingly insignificant stressor as an incision!
There are also three types of depression along the neurotransmitter lines, and plenty of controversy in medical communities as to which is more predominate with depression: low serotonin (leading to obsessive thoughts/ruminative type depression), low norepinephrine (low energy type depression), and low dopamine (low pleasure/motivation type depression). There's also a potential danger of just flooding the brain with serotonin by inhibiting reuptake via an SSRI, *even if* you have low-serotonin type depression (which could in a direct or indirect way be influencing testosterone levels), given that serotonin and dopamine work against one another, meaning you could lower your dopamine levels as serotonin goes up, causing more balancing problems.
I'd say find the root cause behind low T and depression, but that's way easier said than done.