What Could A Persistent Soft Lump Under My Chin For 6 Years Indicate, Especially Since A Second Lump Appeared And Disappeared Within 2 Weeks?

Hi I have had a lump 1.7cm present under my chin for 6 years now. I first noticed the lump six years ago …1 week later I noticed another lump which was hard but it disappeared in 2 weeks,the soft lump however is still there 6 years later .what could this be?