All of these Psalms are from David during his times of hardship. Most of them occur when he is in a desperate state and is pleaing to God for either help or answers. His desperation becomes apparent in Psalm 55. He is betrayed by people who have tried to help him and says that he can trust no one other than God.
Psalm 51 is about confession of sins. However, before looking at the context and seeing that David was speaking, I had thought it also could be about original sin. In verse 5 he states, “Indeed I was born guilty, a sinner when my mother conceived me.” I did not think original sin was apparent until Jesus was baptized, however maybe this is an allusion to something that will occur later on in the bible.