I don’t know what’s wrong with your sister. I do know that her behavior is unacceptable. Where are your parents? How is it that she is allowed to hurt you? If she is living in the home, your parents have the right and obligation to tell her that she can’t behave like this. You (and her son) deserve their protection.
My only guess about the way she treats you is the same as yours — jealousy. It may be very painful to watch you have a life that is so different from her own. She had a baby when she was only 16. She may regret her choices. She may feel that she missed out on the fun of being a teen.
Go to college to get an education, not to get appreciation from your sister. Whatever her issues are, it’s unlikely that seeing you move forward in life is going to cause her to think differently.
Meanwhile, I hope your sister is getting some therapy and some parent education. She is only 20. She has a long life ahead of her. She will do herself and her son a big favor if she takes care of her issues now so they both can be happy and healthy.
I wish you well.