Lumps following breast reduction are either areas of scar tissue or areas of fat necrosis, neither are worrisome. You should have had a pathologic exam of the removed breast tissue from the reduction and the results should reassure your that the lump are not a problem.
Always have breast lumps evaluated by a Dr. Having said that it is probably residual from ur surgery and it is common to have some lumps and bumps. Lots of nodes and fatty tissue in there and they do go through swellings and trauma from surgery. Get it checked out though!! Just don't worry!
Seroma