The actress, who played Lavender Brown in the Harry Potter series, is having her fourth child and said the symptoms of the virus have lasted weeks.
Cave, 34, shared the news with her 200,000 followers on Instagram.
She wrote: “Triage, once again… Anyone else had covid in 3rd trimester & had it hit them like a tonne of bricks for weeks?”
In a second post, she added: “Also – has anyone taken the anti-nausea drug and it made them feel worse?”
On February 19, Cave said she had Coronavirus and Norovirus and her pregnancy was leaving her nauseous.
The actress is in a relationship with comedian Alfie Brown and their children were born in October 2014, July 2016 and October 2020.