Hard sore breast

I have no clue what’s happening or how to stop it. But im done. I’m 16 weeks, my daughter was EBF from one side for the last few months, before obviously both. Anyways she’s officially weaned. The last month, the breast she hasn’t eaten on in months is hard and sore. It looks normal, but the breast she usually ate off of is soft and not hurting at all. What can I do? Is it the pregnancy, is it drying up the rest of the way? It’s rock hard. I took antibiotics for a possible infection but nothing. Please help 😢