You have Puberphonia
,ie.,a persistence of childish voice into puberty
and sometimes beyond,if not attended to earlier.You need counselling
and speech therapy
.You can chek improvement in voice by doing Gutzmann's test..stand in front of a mirror and holding your Adam's apple,press it backwards,bending neck a little and say your name..see how the voice becomes masculine.keep doing this daily for half hour and you will start talking llike this itself.If notbetter get the help of a speech therapist.