How can i fight off constant feelings of despair from thankless job?

Thankless job: Focus on staying productive & praise yourself for that.

Change a job?: Try to focus on positive aspects of your work environment -- make a list and put it in front of you when you experience feelings of despair. How about looking for another job, talk to a career counselor-- re-evaluate your feelings related to the job -- did you feel this way before or something changed? Good luck!

Must change: For your mental health, either change the way you appreciate the job or change job. Not so much other people thanking you for the job but even more importantly, whether you appreciate the importance of the job. Why should you waste your life on work that you don't see as useful to anyone? Look for another job that you think will be better. Give it a try.

See below...: Look at changing jobs... Until then, explore and focus on positive feelings that you get from areas of your life where you do feel more appreciated. Remember the law of attraction: to feel appreciation, think thoughts of appreciation... Good luck!