Trekker, you mentioned you're already seeing a psychiatrist and taking meds for your depression. I, too, have been on an anti-depressant medicine for years (mostly for my anxiety). But sometimes I still can't help feeling stressed out, anxious, or just overwhelmed by everyday things.
When it gets to that point, I've found that
meditation really helps me focus and find a balance. When I first went through depression several years ago, my former boss was a very thoughtful and supportive person who recommended meditation to me. You find a quiet place to sit down and focus on your breathing and clearing your mind. There are different variations,
Qi Gong being one of them. She and my other lady friend were also very much into Eastern philosophy. Although I'm a Christian by faith, there's much wisdom you can find from reading books by the Dalai Lama. I believe there's one called the
Art of Happiness. You can do tai chi and yoga as well, which are both beneficial to the mind and body.
I would echo what someone else suggested about finding a hobby, something you are or would be interested in. It would help you focus your mind and energy on keeping busy and being creative at the same time, e.g., arts and crafts, taking pictures, collecting coins or other items, etc.
You mentioned you've given up on relationships. I can sort of relate to this, but then again, my situation is a bit different. I was a "late bloomer" to begin with, and when I started dating, I was in my early 20s and haven't been in a relationship since then. I'm totally OK with it. Perhaps what you need to do is not actively seek out a romantic relationship. Just try to focus on meeting people for now--going to social events, volunteering, networking. Two of my best friends in the whole world are happy living by themselves. I've mentioned this before--one's a bachelor in his 70s and the other is a divorced woman in her mid-60s, all happy with family life and being independent.
Life can be beautiful, too, if you focus your energy and attention outwards instead of focusing on your needs. I'm diabetic, I've got a host of health conditions, and just yesterday was diagnosed with
Posner-Schlossman. But I'm trying to stay positive. We only have one life, and it's too short. Better make the most out of it while you can.