Hi, I Found A Lump Under My Skin A Week

Hi,
I found a lump under my skin a week ago out of nowhere around the area i think Tensor Fascial - I had had a weight workout a few days prior and also the day before I did a stair run/walk approc 500 stairs when i misjudged a step and stepped heavily on the ground - could this be injury related or something more to look into. It isnt really sore to touch , only tendor after prodding it for a while! not rock hard or too soft either. thanks