I have low voice and get puzzled when speaking english?

im 17 and im a quiet person, ive been like this all my life, i speak english with my mates, in school, college, etc, but most of the time as im quiet i speak my home language, and i have a low voice as well, some times people ask me what, pardon, sorry, its cos i either speak in low voice or i get puzzled when speaking english, im starting to worry, as im nearly an adult i need to start talking alot and act like an adult. what can i do? i find it hard to speak louder cos i aint got the strength, and im also skinny so i dont know if that affects me.