Dr. Shahryar Tork is fed up with rumors suggesting he's the reason for TikToker Rachel Tussey's death ... and he's now going after who he thinks really caused it.

In a new lawsuit, obtained by TMZ, Dr. Tork blames JourneyLite Surgery Center for Tussey's passing because he says they never provided safe recovery and post-anesthesia care.

According to Dr. Tork, the initial surgery went "smoothly" with him, but things went south during her post-op care with the Cincinnati surgery center, which he claims offered an unqualified care-unit nurse who ended up administering a post-anesthesia opioid overdose. He claims two of the surgery center's nurses "administered more opioids in a period of minutes than Mrs. Tussey had needed during the entire nine-hour surgery." He says this opioid overdose caused a respiratory failure that led to Tussey suffering an "anoxic brain injury" -- essentially a lack of oxygen to her brain.

Dr. Tork says he is bringing the suit "to ensure that the truth comes out and that no other patient and no other patient's family suffers the same tragedy."

As you know ... Tussey died in March following a tummy tuck, liposuction and umbilical hernia repair.

She was 47.

RIP