Looking for this song that makes me mad... :'(

[shippo]

OK, I heard a song, a really catchy song in radio...
It have some kind of "tararam tararam" for the lyrics in the front of the songs...
and for the reff the first sentence is "it's complicated...." and after that sentence, another sentence being followed that rhyme with complicated

Ok, this song drives me crazy cause simply I DON'T KNOW the artist/ even the title, and it being played few times in radio here... Well, the DJ HAD mention the song title & artist, but because my BAD english, i can hear it clearly.... It sounds like "Imagine If" and "Louis?" and "X"???

PLEASE PLEASE, i know it is extremely vague by this explanation... But ANYONE KNOWS what is this song??

I try to google "It's complicated lyrics" But, Avril Lavigne that gives the most result...

THANK YOU....

Oh yeah, it is sung by a woman...