There really isn't any other way, than to find the strength and courage to tell somebody how you feel. Your mom actually from your short message sounds quite nice, in that she was willing to ask what is "wrong" with you and was willing to find a therapist for you. I would discuss the matter again and ask that she would find a therapist, which is specialized to gender issues. Discuss the matter in a calm way and explain how you feel. She might not understand immediately, but I do think it will at least give something to think about for her.
I can't really comment the school counselors or GSA as I have no experiences from those, living in a different country. But I do wish you luck and above all, courage to be who you are and find somebody to talk to in person.