The 51-year-old, who was sentenced to 17 years behind bars back in 2023 for her role in a fatal car crash, says just after she was relocated to Lowell Correctional Institution in Marion County earlier this year ... she noticed something wrong with her left leg.

She said she began to experience severe swelling from the top of her knee all the way down to her toes, and immediately sought out medical attention.

But, she said for weeks, officials at the prison gave her the run-around ... this despite her leg looking "like somebody put a bicycle tire pump on it and just inflated it twice the size."

Sytch -- who is diabetic -- said things got so bad with the extremity, it turned "funky colors" -- and at one point, it even developed a "huge red lump right under" the calf.

"I could barely walk on my leg," she told us in an interview from prison last week.

Eventually, after days of complaining, she said she was able to get testing done ... and was diagnosed with a blood clot that needed blood thinners for treatment.

However, she said even getting that medication into her body has been a chore ... and she's worried how prison officials are going to care for her as she tries to heal.

So far, she appears to be optimistic ... but she told us if things keep going poorly -- she's going to insist that she receive care at an off-site hospital.

"All that's been going through my mind for the past three weeks is, 'Oh, my God, I'm going to follow in [my ex-husband's] footsteps and die of a blood clot just like he did because I can't get medical treatment at this prison,'" she told us.

"It's pretty bad."