Baby not feeding

Hi, my 26 week old girl recently developed a fever. Spoke to the doctor gave her some paracetamol, fever went away in 24 hours. She started rejected my breast milk when she got the fever. So I gave her formula. However now 3 days later she has no fever and she is still rejecting breast milk and only having formula, is it a phase.. can I get her to take breast milk again. She completes 6 months tomorrow so we would start solids for her soon. I really want to continue her on breast milk. Please help with any tips. Thanks in advance