I'm 18 And Two Days Ago I Started Bleeding After

I'm 18 and two days ago I started bleeding after I urinated only when I wiped though. I am on birth control pills. 6 months ago I took depo shot for 2 months I've been on a pill since with the blood I noticed a giant clump of something that looked clear and bloody when I urinated this has only happened once and a small few pieces twice but spotting off and on when I wipe what is this