I had something similar earlier this year. I lost 12 lbs in a couple weeks and I suffered with fever and nausea. I finally went to the hospital because it felt like my skin was on fire. The said it was covid, go home.
I called bullshit and did a round of antibiotics thinking it was a staph infection based on the symptoms.
The antibiotics took care of the burning and I was able to drink ensure to keep from losing more weight.
All is good now.