I was born in a Muslim Asian family and wasn’t brought up with much islam and I left my religion as I never understood anything and now that I’m 19 I took my shahada again and I’m more on my deen now, will it be counted as a sin, I mean my past?
Not at all. In fact, the Quran says that those who repent and come back to faithfully worshiping God will have their past sins written as good deeds for them.
Except for those who repent, and believe, and do good deeds. These—God will replace their bad deeds with good deeds. God is ever Forgiving and Merciful. (The Quran, verse 25:70)