What Causes Lump And Bruise On The Tip Of Elbow?

Hello. I had a large lump appear on the tip of my elbow,felt like fluid filled. Bruised all the way around elbow when lump went down. Three weeks later, two days after bruises went away,another lump( same as before) popped up and now bruised all the way around again. Any suggestions on what this could be? And no injury to elbow, didn t hit it or anything like that. Thanks Crystal Blackwood