Would it be problematic to switch to a different marja due not knowing this? I have been muslim for a year and a half. However I’ve only been shia for a year so do i need to make up the prayers from the months i was sunni for at the beginning of my conversion to Islam?

I didnt there think there would be a ruling about this and I remember asking some friends and they thought the same thing, so I never thought anything of it

When you were Sunni, if your school of thought considered your Ghusl to be valid then you don’t have to repeat your prayers.

As for switching, if you believe another Marja’ is more knowledgeable in this ruling then yes you can switch to another Marja’ in this ruling (or entirely if you believe the other marja’ is more knowledgeable in general)