I also struggled with regrets a lot, still do when I am tired or when something is bothering me. But I think it is important to forgive ourselves. At the time we lacked knowledge about ourselves and others, and we CAN learn from our mistakes and make amends to the Universe, if we can't ask for forgiveness from others. Helping and supporting others, developing new skills and so on have helped me a great deal in dealing with my feelings of guilt and shame.
Also, replacing these persistent thoughts about how bad I was with phrases like "I am making amends to the Universe" for instance has been helpful. It will take some time to reframe our thinking, but I think it can be done or at least you may feel lighter after a while.
I would encourage you to share, Happy Poo. Remember that the Cs told us to network! Also, I think that I wasted a lot of my precious energy going round in circles and it didn't get me anywhere, because I was still too focussed on myself. When I stepped out of that cocoon of guilt/regret so to speak and focussed more on what is in front of me and others things got better.