Purple Lumps With Pus Under The Skin, With Red And Black Dot In The Centre After Popping. History Of Ring Worm In Those Places. Biopsy Needed?

Hi, I aquired a very serious ring worm at the beginning of January this year from a stock show lamb. 5 months later, the ring is gone and is just a scar now but I have these purple, under-the-skin lumps in that place that when popped, have pus in them. After they are popped they are still pinkish purple but now have a perfect reddish/black dot right in the center of them. Should I go have these bumps biopsied? What could they be??