Pink is stressed out about having another child.

The 'So What' hitmaker, who has four-year-old daughter Willow with husband Carey Hart, is reportedly struggling to get pregnant again and is doing everything she can to stay healthy.

A source close to the 35-year-old singer told US OK! magazine: ''She's taking folic acid and putting on weight to boost her fertility. She wants this more than anything, so the situation is very worrying.''

The star recently hit back at critics for suggesting she had put on weight and insisted she is very happy.

She said: ''I'm not worried about me. And I'm not worried about you either.

''I am perfectly fine, perfectly happy, and my healthy, voluptuous and crazy strong body is having some much deserved time off.''

But she later admitted the comments hurt her feelings.

She said: ''I don't take well to bullying. I never have. I'm not a person that will be bullied. I'm not a person that will stand by watching other people bullied.

''I'm raising a girl. I am a girl. I have feelings. People think I take no s**t and I'm tough, tougher than nails, but I'm a human being.''