hi mogli, i am not an english native teacher.
your problem is like what i had.
firstly, i couldn't speak english fluently and i always had difficulty in speaking. i had got bad remark in speaking when i was in college. i was always confused in choosing what grammar i should use. consequently, i made many pauses just to make my speaking grammatically correct. when i talk to my friend, it would be OK. but, in front of the students, it would be horrible.
i realized that i have to be fluent in speaking english!!
to make fluent in speaking english, we have to talk a lot. babies always talk, they don't think whether they are grammatically correct or not. the important thing is they talk and try to make people understand what they mean.
so, to make we fluent with english, the important thing is talking a lot. don't be bothered with the grammar. we can speak mother tongue, because we don't be afraid of mistakes. it doesn't matter your grammar is not correct. the important thing is you can speak flently and people understand what you mean.
for that reason, i tried to talk a lot. i set my mind with english and practiced it with my english teacher friends. we had commitment to not speaking with our mother tongue, even in long coversation.
then i had confidence to speak english. while i was trying to make my speaking well, i was trying to construct my words right.
i tried to speak english all day long. to peer teachers, to students, i tried to speak english.
to win confidence in front of the students, just remember: we are teacher, they are students.we have better english than the students. they will not understand whether we are right or wrong
(this thought is bad actually, but it is useful to make us warm/not nervous in front of the students
). try to pay our mistakes by finding the correct words to say in another chance.
it is hard. but, we can make it if we think we can. don't give up. little by little, with lots of practice we can make it. trust your self.