Late GF's Mom Says Jim Carrey Had STDs

2:35 PM PT -- Jim Carrey's lawyer, Marty Singer, tells TMZ: "This is just another desperate attempt by the attorney after Cathriona White’s own family distanced themselves from this sham lawsuit yesterday. These distortions and false statements by the attorney do a disservice to Cathriona’s memory and to the truth. Cat White’s biological mother, Brigid Sweetman acknowledged in writing that she received death threats because people believed she was responsible for Cat’s death. This latest attempt to create a diversion by the attorney from his meritless claims just shows how low he will stoop.”

Jim Carrey exposed his late girlfriend to herpes, chlamydia and Hepatitis A by hiding it and continuing to have unprotected sex with her ... according to new docs filed by her mom.

Cathriona White's mother, Brigid Sweetman, claims she has Carrey's positive blood test results and submitted them as evidence to prove he knew he had STDs in January 2013 ... a couple weeks before he was with Cat for Valentine's Day. Even worse -- Sweetman alleges Carrey infected Cat and then played dumb when she told him she had "bumps down there" and was going to get checked out.

For the record, Jim Carrey adamantly denied he transmitted any diseases to Cathriona.