I have a large infected spot on my aerola which is sending shooting pains through my breast, some puss has drained from it and its very tender and hot?

Mastitis: Sounds like you might have mastitis, a skin/tissue infection of breast. Since you're in the UK, it's time to see your GP for antibiotics. In meantime, warm compresses are recommended for infections (while ice packs are for injuries). If possible, use ballpoint/ink pen to outline reddened area of infection. If redness spreads despite warmth before you can get to GP, go directly to closest A&E.