2 questions about singing?

OK, these are my problems/ questions.

1: I can memorize lyrics amazingly well, even after listening to a song 2 times and can remember them for over a year, and go right to the song again. I control my voice very well, and can hold and make notes higher and lower (not sure how to say it). Theres only one problem… My voice is CRAP! any advice?

2: Whenever I sing, no matter what time it is I feel like yawning, it also happens if I give a lecture or mini speech. What gives?

Yes, I am a guy, I’m not sure if my voice has changed, I haven’t noticed but people say it has. I am 15, and i do have asthma.
If you need ed anything else let me know.

Any help is appreciated.