First of all, I haven't read through all the responses, and I apologize if that is bad etiquette (sp?) or if I have missed something, but I just wanted to answer quick. When you describe how you feel, I remember how, when I was little, my mother was always mad and yelling. One day (as she tells it) I told her she looked like a monster and she realized she needed help. She began taking anti-depressants, and was on them for many years. They were not a miracle cure, but they gave her the edge she needed to cope and begin to enjoy life again. What you describe sounds exactly like she says she felt. It also is almost a textbook description of depression. I think you should continue taking your anti-depressants, because it takes awhile for you to feel the changes they make on your brain chemistry. I should also advise you to continue with therapy, but I felt like I never made progress with a therapist (yes, mental illness runs in my family). Eventually, once you are stable, I encourage you to look into alternative treatments (supplements, etc.)--for some people they can be VERY helpful (more so than with traditional anti-depressants.
As for your son, I am not a doctor or any kind of "expert" to give you "professional" advice. I am, however, a teacher, so I do have experience and training in recognizing potential problems, and I think your son may have some issues to work on as well, some relating to your own problems (not feeling at the top of your game can affect parental guidance) and very possibly physiological issues (ADD?).
Please remember, though, that you have not done anything to feel guilty about. If you haven't been the best parent, well, you have been struggling with a bona fide illness (depression is not psychiatric mumbo jumbo, it is a treatable physiological disorder!) and once you are back on your feet, things will begin to get better for all concerned. Take it from a child who was once in your son's position: things CAN get better!