Can fatty cysts be painful? Mine is tennis ball size by left scapula; have constant left back pain & occasional left chest pain.

Yes. I am assuming you are talking about a lipoma which is a benign fatty tumor. Regardless any mass the size of a tennis ball should be looked into. To answer your question yes it could cause pain. It can be putting pressure on a nerve or structure which could hurt. If its a lipoma then outpatient procedure.
Many possibilities. Some causes of painful “lumps” may include: bony overgrowths, soft tissue masses, ganglions, fibromas, and cysts. Have it evaluated by a professional to get the right diagnosis.