Hey S, I know that feeling so well. I want to reassure you though, that you can get out of this slump. Check the dosage of your meds with your doc. You may need to adjust it. I found I had to do that because besides the crappy, low feeling everyday, I was still having some side effects several weeks after starting my new meds.

Keep trying stuff you used to enjoy doing. You'll find something worthwhile, if you keep at it. And please, keep a couple close friends near to you and get involved in outdoor activities with them as much as you can, despite how you feel. Allow them to push and encourage you. It's worth the effort. You can get out of this slump. And by the way, I'm going to be 40 in a couple months, so I understand your concern about age. Don't let that stop you! There's lots more life left in you!
Lots of hugs