Shalom, is it true that in the Midrash Hebrew the forms -cha and -ach are both male and for the female form the yod is used, like -ich? And what about the two forms to adress G-d in the siddur, -ach and -cha: are they both male?

G-d is referred to in the masculine gender. The feminine gender is not used in relation to G-d because G-d is an active force in the universe. (See Akedat Yitzchak Gate 4, The Handbook of Jewish Thought by Rabbi Aryeh Kaplan zt"l, pg. 13)