christmas I really hope you will decide what is right for you and your dd.
"My mum was very ashamed and still is 5 years later. She called me a slag, now it's going to be even worse."
NO, it is not going to be worse because you are an adult and this is your life, it is not her choice!
"In my heart I would like to keep the baby" GREAT - CONGRATULATIONS that is all you need to know.
"Im scared of having the dad involved in case he thinks I'm not good enough, I'm scared of someone taking my baby away from me, I know that's stupid." It is not stupid to be worried but I don't think you have anything to be worried about.
Do you think he deserves to know? If so, tell him. Just say, I;ve found out I am expecting a baby, your baby, I know this will come as a shock, it is to me too. I want to keep this baby and I felt you needed to know. I wanted to know how you felt." Or words to that affect.
BUT however he feels, the choice to keep the baby is yours.
He might be over the moon, he might run for the hills, but whatever he does it is what you do that will really matter for this little one. You've proved yourself. YOU CAN DO IT!
And your mum, say something like...
"When I told you about dd, your comments were really hurtful.
I am expecting again and I wanted to share this happy news with you. If you are not happy about it, that;s fine, but i am delighted dd will have a baby brother or sister." Or words to that affect.
I might introduce the idea of the boyfriend first "By the way I am seeing XYZ now." But you do not have to.
Its not your mum's business, you are an adult. Congratulations.