Why do I feel like I'm either singing too high or too low all the time?

If Im singing a song while listening to my iPod, and the artist has a
higher pitched voice, my voice sounds too deep then I feel like I
can't sing it... But when I go to my head voice it sounds it sounds
like Im in key... But when I shut my Ipod off and sing the same song,
it sounds like my voice is way too high pitched... Could anyone help
me with this problem??? And how do I fix it? please and thank you!!!