Hello northsea and thanks for posting,

I'm afraid I don't know if this recent shoulder and collar bone pain are linked to the breast lump and redness, they may not be so try to keep an open mind until you can talk to your doctor and ask them what they think. 

As you have been prescribed antibiotics, I assume your GP thinks this is an infection. The NHS website information for mastitis (breast inflammation which can be due to infection) says to go back to your GP if your symtpoms don't start to improve after 2 days of taking antibiotics, so as this is the general advice, I think you should follow it and contact your GP practice this afternoon. 

I hope they can help.

Best wishes,

Julia