How do I get over this feeling of shame, regret that I get after I do anything to help others who don't appreciate it?

Therapy may help. It is unusual to feel shame when others don't "appreciate" help you've offered. If this is a longstanding pattern, it probably has roots from your childhood. Therapy to understand why this pattern repeats itself can lead to freeing you up either help folk who do appreciate it or accept that not everyone can accept what you have to offer.
Shame. Shame is just about the darkest emotion people can face. It presupposes that there's an audience to our alleged wrongdoings, and that devastating judgement will be passed. Something to remember is that everyone has something they feel ashamed about; it's inescapable. Find a reputable psychotherapist to speak with. Getting it off one's chest in a safe, nonjudgmental place is the first step.
Helping others. These are inevitable feelings. Shame is a necessary physical feeling that tells us things aren't going the way we want. In general we should reach out but a necessary part of life is learning that people have their own desires , their own wants and are contrary. You may be pushed to help others out of some need that is unhealthy and so you overdue it? Talk to someone.