Serving Christ can be agonizing. Jesus said it himself, "Blessed are those who are persecuted for righteousness' sake . . ." (Matt. 5:10).
Especially for those working in called ministry positions, there is a weight. A burden. A cloud of pressure derived from spiritual forces under responsibility which has eternal consequences.
You've asked, "How much difference am I making? Should I go on? Should I give up? "
Here is some help from 19th century English preacher Charles Haddon Spurgeon. The following is from his Lectures to My Students.
The School of Adversity
By all the castings down of his servants, God is glorified, for they are led to magnify him when again he sets them on their feet, and even while prostrate in the dust their faith yields him praise.
Glory be to God for the furnace, the hammer, the file. Heaven shall be all the fuller of bliss because we have been filled with anguish here below, and earth shall be better tilled because of our training in the school of adversity.
The lesson of wisdom is, be not dismayed by soul-trouble. Count it no strange thing, but a part of ordinary ministerial experience. Should the power of depression be more than ordinary, think not that all is over with your usefulness. Cast not away your confidence, for it hath great recompense of reward.
Even if the enemy's foot be on your neck, expect to rise and overthrow him. Cast the burden of the present, along with the sin of the past and the fear of the future, upon the Lord, who forsaketh not his saints. Live by the day - aye, by the hour. Put not trust in frames and feelings. Care more for a grain of faith than a ton of excitement. Trust in God alone, and lean not on the reeds of human help. Be not surprised when friends fail you: it is a failing world. Never count upon immutability in man: inconstancy you may reckon upon without fear of disappointment.
March in the Dark
When your own emptiness is painfully forced upon your consciousness, chide yourself that you ever dreamed of being full, except in the Lord. Continue with double earnestness to serve your Lord when no visible result is before you. Any simpleton can follow the narrow path in the light: faith's rare wisdom enables us to march on in the dark with infallible accuracy, since she places her hand in that of her great Guide.
Between this and heaven there may be rougher weather yet, but it is all provided for by our covenant Head. In nothing let us be turned aside from the path which the divine call has urged us to pursue. Come fair or come foul; be it ours, when we cannot see the face of God, to trust under the shadow of his wings.