What Causes Cystic Acne With Smelly Liquid Discharge?

I have been diagnosed with cystic acne. I get large painful knot filled with clear smelly liquid that have been there for over 3 yrs. Sometimes they have bloody liquid inside too. They slowly get larger and sometimes they itch. I think it mite be something more like a bacteria or parasite. I had clear skin till 25 & it developed and hasn't quit since.