Poor thing. 
That must be so rough for you, not knowing what is wrong.
I hope you can take some comfort in the fact that you are making a good choice by not allowing him to suffer. One of the most important parts of being a pet owner is making the choices your pet himself cannot make. When you know he is not going to get better, and he is not experiencing a good quality of life, the kindest thing you can do is end his pain for him in a gentle way.
It's a difficult thing to do, but it's the right thing.
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2.0 bearded dragons (Ocho / Domo-kun)
0.1 kingsnake (Rio)
1.0 ferret (Playstation)
1.0 cat (Wally)
0.1 dog (Tima)