I was in hollister today it is december 2009. I heard this super cute song it is sung by a woman it mentions happy in it often. It isn't rock or anything like that. It was super cute please try post all the songs you think are possible answers. Thanks!
I believe this is their current playlist (it might be missing a few but oops): (At the one I shop at, I had a friend give me this she works there lol)
julian casablancas – 11th dimension lifehouse – make me over julian peretta – wonder why amy mcdonald – mr rock ‘n roll rob thomas – mockingbird metro station – kelsey colbie caillat – running around jason castro – let’s just fall in love again kenna – say goodbye to love justin james – perfect sometimes o.a.r. – something coming over relient k – silver bells sherwood – make it through we the kings – heaven can wait five times august – do it again leslie mendelson – so far so bad black kids – i’m not gonna teach your boyfriend how to dance with you
Hope this helps. Good luck =]
merry happy - kate nash? thats my best guess :)