What is this?

what is this thing
That beats in my chest
What is thid thing
It is becoming a pest

What is this thing
Why won't it go away
What is this thing
It better not stay

What is this thing
I just don't know
What is this thing
Why can't it just go

What is this thing
That makes me love
What is this thing
This thing I can't get out of

What is this thing
It drive me mad
What is this thing
Is it all just a fad

What is this thing
I've hated from the start
What is this thing
This thing called my heart