I've today had a very sore, painful armpit and there is a lump under the skin about the size of a broad bean. It's really tender and painful. I'm breastfeeding but I am sure it's nothing to do with the breast, I know all about mastitis as I'm a breastfeeding peer counsellor lol. I have M.E. but I've never known my gland swell this much before, or be this painful. Help, I'm scared it's lymphoma or something!!