This is the day the Lord has made. We will rejoice and be glad in it. -Psalm 118:24
When reading through the psalms, we can notice that the writers situations were often out of hand, or their sorry or guilt was overwhelming. The writers wrote their psalms to God, telling him exactly how they felt, often crying out and questioning why they were in the situation they were in.
Something important to note was that they were completely honest with God, telling him exactly how they felt. But as they talked with God, their prayers ended in praise. God had given them a reason to rejoice and they praised God for that.
When you don’t feel like rejoicing, tell God how you truly feel. God will give you a reason to rejoice. God has given you this day to live and to serve him, be glad and praise him for that!