My impression of your situation is similar to @canidmajor‘s perception – you became comfortable with being belittled, so it feels awkward to be liked and appreciated.
When someone is repeatedly given negative messages about themselves, they start to internalize the message that they are beneath others and not deserving of positive attention, friendship, love, or happiness.
When one’s self-esteem is lowered, their expectations for themselves are lowered, as well. It’s human nature to seek the path of least resistance, so upon receiving approval the person’s view of themselves is challenged, and that is uncomfortable. Now there are people who genuinely like you, and there’s a new set of expectations to live up to, but you doubt whether you’re capable and you feel like you aren’t really the person that they perceive you to be. This brings self-doubt because you aren’t entirely sure that you can live up to this perception that others have of you.
I understand this challenge and I still struggle with it as I approach 50 years of age, because I was belittled by family members from my earliest moments. It is to your benefit that you are having success and finding acceptance at such a young age, and that you are in a new environment away from the toxic bullies. You didn’t deserve to be bullied and you might want to consider that they bullied you because they saw something in you that intimidated them. Most bullies put others down in order to lift up their own weak esteem.
It will be a process, and some days will be easier while others will be harder, but you’ll get to a point where you have a sense of integrity that allows you to fully appreciate and embrace being happy.
Also like @canidmajor, I am disappointed by some of the replies you’ve received, since your question seems to be a sincere request for help.