Odd tissue discharge- what could it be?

Question

Hello! To preface this I am 18, I don’t menstruate and have had Nexplanon for a year which is how long I haven’t had periods. I had UTI symptoms, got Bactrim for it, and on the fifth day of treatment started bleeding and having clots. ER said I had passed kidney stones and the blood was from my urethra but I seriously doubt I peed this out. Any ideas?

Answer

Looks like uterine lining to me. (Period) even though you haven’t had a period in a year due to nexplanon, you can start bleeding anytime on it.
This was my experience while on it as well.  
However if you are super concerned call and make an appointment with your doctor. :)