Another vote for CBT. CBT has made a big difference for me, helping me to find my way out of some very negative patterns of thinking, and allowing me to feel real joy, despite a number of ongoing difficult circumstances in my life. I'd recommend it to just about anyone, at any age.

I didn't go through CBT with a therapist. I just read the first few chapters of The Feeling Good Handbook, then tried to establish a habit of confronting my negative feelings, and the thoughts that were feeding them by identifying the distortions in those thoughts.

YMMV, but it may be worth a try.