Hello,
Welcome to the forum. Such kind of lump can be swollen lymph node, boils or abscess, cyst, hematoma formation after muscle strain or a benign tumor. For the confirmation of diagnosis, you need to get this lump examined from a doctor and get a MRI scan for any soft tissue growth (to rule out any tumor) and a FNAB (fine needle aspiration biopsy) done.
Till then, apply warm compresses on the bump and keep the area clean. You should consult a doctor as you might need a course of antibiotics/anti-inflammatories to take care of the same.
I sincerely hope that helps. Take care.