I second the ultrasound from the physio.
Also is something poking on that spot (a bra, your elbow while you sleep, DD's knee while she's in a carrier.......)??

Lecithin can sometimes help with blocked ducts too.

And gentle on the massage - sometimes massaging too hard can cause inflammation, making the blockage worse. You shouldn't need to massage hard, and probably not even firmly - more like cat-stroking level or lighter.