You need to change things up a bit - I found this used happen to me when I had nothing to look forward to - now i just make sure I always have something fun/interesting planned in the near future !! Whether it's a holiday, night out, concert tickets, festival tickets, theatre - then I don't mind the weeks i'm broke, sitting at home only working & sleeping - the knowing something is coming up makes me happy!
Also if you don't like your job or something then find something else!
I hit rock bottom at 21 when my long term boyfriend left me, i lived at home, felt lost, finished UNI couldn't get a job, lived with my parents - I saved up for a year and moved away to Canada on a working visa for 12 months!
Came back, was at square 1 again - in my parents, looking for a job etc - met my boyfriend (now husband) we were feeling a bit lost - saved up and went backpacking for 6 months and then moved to a different Country on return and started a new life together!
What would make you happy??