I have an adopted dau who suffers with bipolar disorder.
When she first received the dx, I went into "helper" mode and go in and out of this mindset. However, I realize that as very hard and unfair as her burden is, it is really her burden to overcome. It is this way for us all in life.
What you have mentioned is something that sounds very familiar. I have seen her suffer in this way for many years....even when she was a young child.
Even today. On the positive side, today I feel she does slightly better because even when she is depressed (perhaps not in a deep depression), she will pick herself up and go to a store or restaurant and get out of the house.
My thought for her was that if she had a volunteer job once or twice a week...something that was not overly stressful, but enough to get out of the house and meet people on a regular basis, it would be very helpful. Most folks greatly appreciate their volunteers and it tends to be a positive experience. Perhaps you could read to the younger children at an elementary school or at a nursery school. Just an idea.
I hope you find something that will help you to feel better soon.