Unforgivness the willful intent to to deprive yourself of GOD'S infinite graces. Quite often people give lip service to forgiveness, but in their heart they hold onto the hatred, anger, and self-righteousness, because these people feel that they are right and everyone else is wrong. Thusly, they have a right to not forgive those who have wronged them. This of course is a lie from the pit of hell. A lie which only makes your life worse and further deepens the divide between you and GOD.
For some reason people think they must feel something for the forgiveness to take effect. Forgiveness has nothing to do with feelings and EVERYTHING to do with willful intent.
Jesus Christ told St. Faustina that all merit lies in the will, not in our feelings.
So, it is with your sovereign will that you must decide to forgive. It is with your willful intent that forgiveness occurs. Your feelings about the person or parties involved may not change right away. That will come with time as you grow closer to GOD. You can, however, ask the Holy Spirit to remove the pain inside your heart towards the person or parties which hurt you. GOD Loves you and wants you to be happy and free. All you have to do is be willing, be obedient, and GOD will do the rest.