HOW TO GET A STRONG SINGING VOICE? 10 POINTS?

KINDA LIKE JANIS JOPLINS:I know I will never be able to sing Just like her or anything like that lol ( people who have heard me sing day i have a good voice.( one time when i was singing karaoke and came down a woman came up to me adn said i was very good up their and another time when i was singing class because i was bored someone heard me and said i should be in the talent show. But I wanna be a rock/ Blues singer like her someday.( I liked singing for years( im 14 year old girl) bu Janis really pushed me into it a lot more. I have a problem though: my lungs and throat are messed up I cough up stuff sometimes and 90percent of the time I cant get it out and if i just drink lets say I had blue powerade after drinking it i will cough up blue stuff. and i have a hard time breathing through my lungs my doctor( been there twice but different doctorsI ughh some doctors seem to thinkantibioticss cure everything) put me antibiotics but it never works. I plan to see a doctor soon but i dont think they can do much other than that. well if i do ever get better( haha) how can I get my voice strong? o yeah and i sang in school fromkinder gardenn-6th grade but i quit because I got sick of the teacher she was kind of a ***** even in Kindergartenn she always yelled at us for acting up sometimes and called us immature we were kindergartnerss for godsakes! lol OH YEAH AND NO SMARTS *** ANSWERS ABOUT JANIS! I will not put up with trolls i will report you and kick your dumb@sses off yahoo answers! LIE DONT BE SAYTNG STUFF LIKE OVERDOSE ON HERION , OR DRINK WHISKEY AND SMOKE CIGARETTES HER VOICE WAS ALL NATURAL SO THEY RASP SHE HAD SHE COULD TURN ON AND OFF LOL