This is an important truth to remember. You don't need to quit the ministry. You just need to reorganize how you are going about it and learn some new skills. Try a fresh approach. Attack it from a different angle.
Discouragement is an attitude and attitudes are always a choice.
I get discouraged when I choose to think discouraging thoughts. But no one is forcing those thoughts on me. We are in a spiritual battle, and the devil doesn't want the kingdom of God to advance. As a pastor, you're on the front line, so you're going to get hit. The devil will attack you with every kind of thing he can think of to discourage you.