Dina Lohan Still Hospitalized ... Family Fears Cancer

7/31/2016 12:30 AM PDT

Dina Lohan's family is afraid she might have cancer ... as doctors remained baffled about the cause of her stomach pain after more than a month in the hospital.

According to our Lohan fam sources, Lindsay's mama has undergone a battery of tests -- at 2 different hospitals -- since she was admitted for treatment last month. We're told she had a biopsy on a nodule found in her throat. She's currently waiting for the results. 

Doctors gave her a round of antibiotics ... believing her pain was caused by a dental procedure gone wrong, but that only worked for a short time before the pain returned.