You need to take her to the vet to get properly diagnosed and what drugs she should have as not all antibiotics are created equal when it comes to nursing animals.
Our last litter from our pregnant stray had to be basically weaned at 4 weeks because our good little baby was feeding and caring for her kittens as World's Best Mom and she was a small cat to begin with and of course coming into nursing not in peak condition (we only got her 2 weeks before her due date) and she developed a fever and infection and would have died if she kept on having the life sucked outta her.
She got drugs and the kittens were giving KMR 2nd stage and were returned to her with full bellies (we couldn't actually keep them separated because the queen freaked out and she needed to stay calm to get better). Because we kept the kittens full on KMR they did minimal nursing while she was getting better. The weaning was more due to her not having anything to give her kittens without dying, not so much her antibiotics (although I believe that was a factor as well)