My left nipple was very tender to the touch and when I squeezed it there's a bloody discharge?

Need evaluation. I suggest you get this examined by your doctor as soon as possible. We need more information about your age& pregnancy/lactation status and how long this has been going on but the fact that it's only on one side and bloody is worrisome and warrant a medical evaluation. This could still be caused by many things but the differential diagnosis are: papilloma (benign), intraductal breast pre/cancer...