Your pastor has spent hours in prayer and preparation time for the delivery of the Word of God. He is trying to stay focused on not only what the Lord has given him for all those who will be listening but on how the Lord wants him to deliver the message. When a person approaches him with something negative, it could interrupt the whole process.
The best way and time to discuss difficult things is on Sunday or Wednesday night after the evening service; however, it is best to make an appointment and schedule an appropriate time to sit down and handle things. This would be far better for the pastor. He has been extremely busy all day long. The difficult matters need a scheduled time where the pastor can give his total attention.
Proverbs 15:13, “A merry heart maketh a cheerful countenance: but by sorrow of the heart the spirit is broken.”