I hear what you are saying. I have been similar most of my life too. I am always getting told I am too serious, negative blah blah. At 45 years of age, I am now heaps better than I used to be, but still struggle with depression and pessimism on a daily basis.
How long has it been since you have had a medication review? Sometimes our bodies can become resistant to the meds we are taking. I am not sure what is in side of the world, but in Australia there is a 12 step program/support group called 'Grow'. They are a support group for those with mental health issues, and although Aspergers/ASD are not mental health issues as such, depression is. I found this group very supportive, so if you could find something similar perhaps that may be a start? There is no easy fix, as you have found out, and it does take work on our behalf, but if you can find some positive, supportive people to be around it may help.
Additionally, I know it sounds corney, but try and find at least 5 things each day to be grateful for. Start with basics, you have a job and money coming in, food on the table and a place to stay, etc etc.
I am sure other people will have lots of other ideas too. You are more than welcome to pm me if ever you want to talk about things.
(((hugs)))
Maz