How Should Breasts Hardness And Soreness Be Treated?

Hi! I have been breastfeeding my third baby for 6 months now. When he was almost 5 months I received antibiotics for infection in my one breast. After 3 days it was fine and I continued breastfeeding...but now every two or 3 days one or both my breasts become hard and sore and I only experience minimal relief when he drinks. What is causing this and would it be wise to take him off at this stage? And what would be the best way to go about it?