Pink had her gallbladder removed in hospital last week.
The 'So What' singer - real name Alecia Beth Moore - tweeted a picture of herself in hospital on May 31 suggesting she had stomach flu, but a source now claims she had to have her gallbladder, a small organ which aids fat digestion, taken out.
An insider told Life & Style: ''At first she had these bad stomach pains and didn't know what it was, and then it got really bad. They realised she needed to have her gallbladder taken out, so she did.''
Despite the procedure she was able to celebrate her daughter Willow's first birthday on June 3 when her husband Carey Hart took her into hospital.
She wrote: ''Thanks family 4 bringing my lil girls party to the hospital all weekend for me. I spose it doesn't matter where u r when u eat ur 1st cake!(sic)''
However, it was not all hard for Pink while in hospital as she did enjoy the pain relief.
She tweeted: ''Maybe it's cause my mum was an Emergency Room nurse all my life - but throw me in a gown and a hook me up to an IV- and I'm a happy girl. Stomach flu sucks but morphine doesn't (sic).''