Haha weird. You figured out melody, but not the chords, lol. See usually I find out the chords, and since your singing over chords, your usually singing certain notes of the chords and that makes it easier for me. And yes, usually when I see songs, the 1 4 5 are how I figure out which key it's in. Helps me solo better. Here's a little advice for figuring out your chords. When you sing over a chord, obviously you're not gonna be singing the same note over and over while your playing the chord, you change the note to different notes. But you can still tell if your on a chord, you can hear the chord being sung over and when it's being changed to another chord. So pick up your guitar. Strum the E chord 5 times, then the A chord 5 times, and the B chord times(1, 4, 5 chords) and hum over each one creating a melody. Try to hear how it sounds when you change from one chord to another throughout the melody. Also to help practice that, just find songs you like that have some nice chord progressions and try figure out when they change chords in the song, then go find the chords from like ultimate-guitar.com and see if you we're write about the chord changes(when it's simply just chords usually they supply lyrics).