When I had big rock lumps when my milk came in a just massaged them in a hot shower, and expressed a bit out to make it comfy but I dont think my body thought it was a feed itms? It never got to mastitis ... Just recently I've had the same thing as dd got really fussy feeding for a few days. Did the same thing and all seems fine.
HTH, and don't beat yourself up, you've done a great job bfing your boy for this long x