Kelly Clarkson says her boyfriend is ''ruining her creativity''.

The 'Stronger' singer - who is famed for writing songs about heartbreak - has been dating talent manager Brandon Blackstock since late last year and admits being happy is changing her outlook when it comes to writing songs.

She said: ''It is killing me. I'm trying to write a tough song and it is coming out like butterflies and rainbows.''

''It is ruining my creativity. I'm writing all this happy stuff.''

Kelly - who only confirmed the relationship in March - says she's only just found the time for romance and admits fans will be shocked when they hear her new music.

The 'Because of You' hitmaker told PEOPLE: ''People used to ask, 'Why are you single?' and I'd say, 'It is not in my schedule.' I'm in a relationship right now and I have time for it. I never used to.

''With my new stuff, people are going to be, like, 'What the hell happened to you.' It has been really difficult. I love it. It's an awesome problem to have.''