Hi and welcome to HCM. Thank you for your query.
This is probably subcutaneous benign lesion such as lipoma
or vascular lesion and it shouldnt concern you but you need to evaluate this by ultrasound
with aspiration biopsy
and then it can be surgically removed.Since this is painful it may indicate that there is inflammtion so antibiotic treatment may be necessary. You should consult your GP about this.
WIsh you good health.