I just remind myself that since God has decided that it’s OK to forgive me for what I did (assuming that I have been to confession), who am I to go against God by refusing to forgive myself?
I think part of the reason we get mad at ourselves is due to our pride. When you tell yourself, “Yeah, I’m a sinner, but I’m really not that bad” and then you do something that is that bad, it hurts your pride because your actions have conflicted with your self-image. The best way I found to get over my pride was learning to humbly admit that I’m just a poor sinner in need of God’s mercy, just like everybody else. Having come from a non-religious background, this was quite a challenge for me and it didn’t happen overnight, but it was so liberating in the end!
As far as the things that were trespasses against others, pray for the persons you wronged, and if there is something you can do to make things right, do it. But once you have confessed your sin and dealt with the situation, let it go and leave it in God’s hands. The devil likes nothing better than to keep us oppressed by reminding us of our past sins, so don’t give him that satisfaction.