I always get the feeling that what I'm doing is meaningless, echoing the words of Ecclesiastes.
And its true. No matter what I do, it can be very well meaningless.
The only thing that keeps me going is that Ecclesiastes 9:10 "Whatever your hand finds to do, do it with all your might, for in the grave, where you are going, there is neither working nor planning nor knowledge nor wisdom." and Col 3:23-24 paraphrases it and adds"Whatever you do, work at it with all your heart, as working for the Lord, not for men."
The other thing is that the greater purpose in it may be hidden from us until maybe decades later. Just think of what Joshua did in prison, unjustly jailed in a foreign country, with no one knowing of his existence. Yet he made do with whatever his hands found to do, being the best servant in Potiphar's household and again in the prisons of Egypt.