My Seroma on Lower Back is Getting Larger, Hardening and the Area Has Started Bruising? (photo)

You need to visit your plastic surgeon who performed the surgery.  If there is fluid present, the fluid needs to come out, either through needle aspiration or drain placement. Followup is very important to successful results.

    Any concerns about hematoma or seroma should be referred to the plastic surgeon and mandates exam with possible drainage.  Kenneth Hughes, MD Los Angeles, CA

Seek immediate insertion of drainage system of recurrent seroma/hematoma before it becomes infected. 

Seromas do not cause bruising.  You might have some residual blood in the tissues that is breaking down and spreading throughout the lympahtic system of the skin.  Hardening in the areas is normal as the fluid has swelled the local tissue, and should resolve over the next several weeks.  A hematoma could be present if you can actually feel a discreet mass.  I would have your back evaluated by your surgeon, or seek a second opinion from a board-certified plastic surgeon.