As others have mentioned, going out, enrolling yourself on a course or joining a club helps and you may even meet new people (you may meet a few assholes, but hey, what you gonna do?). If you can't maintain focus on something for much time, try encouraging a few friends to join you, or find one that already does something you might think it's nice and go together, each other's interest could help one another. I guess traveling somewhere could help too, see the world and all that, but one needs time and I know it isn't cheap, so that may be out of the question.
Those are just medium/big things you could try. Some smaller things to consider, and these can be done everyday, would be eating at that restaurant that for some reason you've never been to, or taking a different route to go to work, or cooking something different, from an exotic dinner to simply switching brands of frozen nuggets. When weekend arrives, see if someone wants to see a movie or something, hang out with friends, or go for a slow walk around the block, notice the trees, birds and the overturned dumpsters in your city.
I can say that some of that worked for me, as I too was/am having some difficulty enjoying life. Setting long term goals helped as well, since, among other things, I am finishing a college course on a subject I dislike and can't stand work related to that, but I will try getting a masters degree and slowly shift the focus to something I enjoy more. I tried drinking too, getting slightly buzzed before sleep helped a little, buuuut I wouldn't recommend it either, though I went to a party and got drunk for the first time in years... I guess I needed the experience (try more things, but don't self destruct, that's my point).
As for another profession, I'm sorry, but I also can only think of a psychologist or a psychiatrist. Sorry to hear that it wasn't effective for you, I saw a psychologist years ago (for a different reason) for some time and that helped me. Remember that I only can say what works and doesn't work for me, and I confess I didn't try a couple of the things mentioned here, so take what I say, if you still need advice from this thread, with a grain of salt. Anyway, finding joy in life is something, I think, that needs to be done rather constantly, it's a bit of a lifelong struggle and yeah, I'm scared too.
...holy shit I'm ranting. Also, where did my color and size tags go? D: