Is it normal i feel like a despicable person?

Basically I just always feel like a monster, a terrible person who doesn't ever deserve anything good ever, I'm never good enough for anything, I don't deserve happiness, all I ever will and should ever get is suffering, endlessly. I'm just an idiot who shouldn't have friends I don't deserve anything I have. I don't want to feel this way but its always at the back of my mind, I recently met a girl, all I can think about is how much better she is than me and how she deserves better than someone like me.

Its not like this comes out of nowhere, I used to be horrible I made fun of people at school, said horrible things to people sometimes even if they didn't deserve it.

But now I want to redeem myself, I try my absolute hardest to help everyone I meet, I never say a bad word about anyone, I help people out and go out of my way constantly, I compliment other people, give money to the homeless, help strangers, help the elderly with their shopping, tell people what I really feel and what they mean to me, help my friends with everything and anything, take on all their suffering and do my best to help them with it to make them feel better and all I ever want is for everyone else to be happy.

So even though I do this stuff and people say I'm lovely, why do I have this utterly overwhelming thing in my head telling me I'm scum, a terrible blight on the world that should just disappear, trying to think otherwise is like telling water not to be wet.

Even when this girl who I admire tells me how kind I am I can't even look her in the eyes.

Why do I feel like I'm such a terrible person, I don't understand!

Is it normal? For the love of god help, I'm so sick of this. I can't stand it anymore.