I have OCD and depression myself, so I can sympathize with how deeply painful it can be. I am truly sorry you are going through depression. My only advice, other than seeking professional psychological therapy, is to focus entirely on the love of Christ, which is infinite, eternal and ever merciful. There is no sin, whether that we do or original sin in the world, that is beyond His power. All sin will dissipate in the end upon His command. Also, try to see your pain as sharing in the Cross of Christ, suffering for the forgiveness of yourself and the world and growing ever closer to God. In this, perhaps the joy and peace of Christ can overpower the depression that this world causes. I pray for the forgiveness of all your sins and that you may be healed, protected from and strengthened against all sin and all problems, particularly your depression. I ask you to pray for me, and I extend these prayers to all those in the world afflicted with mental illnesses. I ask for the intercession of the Blessed Virgin Mary, your guardian angel, and St. Dymphna, patroness against mental illness. God bless.
Under thy compassion we take refuge, Theotokos; do not disregard our prayers in the midst of tribulation, but deliver us from danger, O Only Pure, Only Blessed One.