Something that we discussed in depth at one of the PHPs that I was in was the difference between shame and guilt. Basically, guilt is "I've done something wrong" whereas shame is "I am wrong." In DBT, there's a skill called Check the Facts, so I would want to know if the things that you feel guilt for are things that you should feel guilt for, and if that guilt is productive. The same goes with the regret that you feel. If it's not productive, then let it go; it doesn't serve you.