Please check the following paragraph.
I think English is interesting. I have studied English for seven years since I was a little girl. Before, Ithought this subject is boring because I have to learn a lot of words. But now, Iím good at it and itís very interesting to me.
(Not a Teacher)
Change it to past tense and this sentence is good:
"Before, I thought this subject was boring because I had to learn a lot of words."