Lets see, why would Jonah not enjoy his ministry. Could it be because he did not want to do it? He did what he could to avoid it? He did not understand it? The story of Jonah is not completed in the book of Jonah, nor anywhere else as far as I can tell. However, the last chapter of the book tells of the experience of Jonah in learning God's love for all mankind. What the book does not tell us is whether Jonah learned the lesson, although it is hard to believe that the book would have been written if he did not come to an understanding of what God was telling him. And I suspect that Jonah, after learning the lesson, went forth with joy in teaching God's love. I don't know what Jonah's attitude was when teaching the folk of N. that the city was going to be destroyed. Maybe he was enthusiastic. He sure was disapointed when it was not destroyed, so he must have been looking forward to the distruction. He also was very miserable when he was not fulfilling his mission, and taking a ride by fish taxi.
I suspect there are times in many ministries that the short term effect is not pleasant. Did Christ have fulfillment in his ministry, yet you know the cry from the cross.
I would stand by my suggestion, that if you are not having "fun" in your activity, you are not engaged in your God given ministry. Your definition of fun may be the key.
One more thought on Jonah. We too often ignore the last chapter of the book. I believe the real lesson of the book is in the last chapter. If we could understand the message from God presented there, we would be a more loving, accepting and inclusive people. We would be less interested in condeming others and less pleased in destroying them with words and actions.
Therefore "go forth" with your ministry, and may your mode of transportation not be by fish, real or otherwise.