Sources close to Jamie tell TMZ ... she contacted a friend last Friday, thinking she needed to go to the hospital. We're told she'd been dealing with an ongoing cough that turned into a lung infection, and even complained about her heart feeling weird the week of her death.

An ambulance took Jamie to the hospital Friday night, where we're told her heart stopped -- and although doctors were able to resuscitate her, it stopped again ... and, as we reported, she died early Saturday morning.

Sadly, she was on the verge of a career milestone -- construction of her new salon was set in motion when rent on Jamie's OG place from season 1 was raised during the COVID-19 pandemic. She made the decision to build her own, but that pushed the production of season 2 back by 4 months.

We're told construction finished last Thursday and the new sign, reading "Babydoll Beauty Couture by Jamie Lopez" had just gone up. The plan is to go forward with the opening, once the building passes inspection. Jamie's loved ones want to hold a memorial for her at the salon.

As you know, Babydoll Beauty Couture was founded to service plus-sized women, and "Super Sized Salon" -- which premiered earlier this year on WE tv -- highlighted the staff and their customers. The new salon manager Jackee has started a GoFundMe to continue to grow Jamie's vision.