huge welp on right leg- you have history of trauma
or bleeding disorders
or associated with fever, it appears in the back side or front of knee
, is there itching over welp, if itching &disappear after 2 hours- likely to be -Urticaria
once daily for 3 days, if on back side of knee likely to be backer cyst- its pain less & need Excision, if history of trauma- advice tablet-brufen 400mg twice daily for 5 days, if not subside then advice X-RAY leg AP & Lateral, if bleeding disorders- advice-PT & APTT, bleeding &clotting time, treatment depends on underlying condition, hope my advice is useful to you, thank you.