Lumps in breastmilk causing pain?

Sounds like it could be a blocked milk duct. I had this, which in my case led to mastitis several times. Expressing made the pain worse and feeding relieved it. One doctor I went to see told me it was thrush, another said mastitis. Antibiotics worked miracles. Mention it to your health visitor. In the meantime I am afraid there is little you can do. A warm bath/compress can help ease it a bit. I would definitely say keep feeding as normal until you have been to clinic.