3 days ago I discovered an irritated area under my left breast. A cyst evolved almost immediately and is now at about the size of a silver dollar (US). The redness around the lump and original irritated area is expanding, and hurts. My PA prescribed antibiotics, which I ve been on for a couple of days now, however the cyst is much the same size and the redness and pain has, as I wrote above, expanded. I m wondering if perhaps it may be a sting or bite of some sort? And whether or not it is, should I go into Immeidate Care or the ER if the lump changes or the redness and pain continue to expand?