I don't know if I qualify as young anymore (I'm 37), but seven years ago I had an abnormal pap out of the blue (after years and years of regular visits) that turned out to be cervical cancer
in situ. At that time the onc. gave me two options: hysterectomy or cone biopsy. I chose the latter because I was recently divorced, in a new relationship, and I wasn't sure I was finished having chidren (turns out I wasn't).
Seven years of regular checkups and good paps later I go in Sep. of this year for my annual and gyn can't get a good culture because I bleed as soon as she touches my cervix. This happens on three separate occasions (gyn thought maybe I was just too close to my cycle, so she kept having me come back).
The third time I still bleed but she gets something useful and the results come back normal

. BUT...two days later I start bleeding and passing ginormous clots. Initially gyn thinks it's "normal" (I tell her it is NOT normal, not for me!) Bleeding lasts for a little over two weeks.
Finally the gyn sends me for a pelvic ultrasound where, like you, they see a cyst on my left ovary and my endometrial lining is slightly thicker than it should be.
GYN suddenly decides maybe something is amiss and does a hysteroscopy. The result: invasive cervical cancer. (Which is why I'm now recovering from a radical hysterectomy.)
Moral of the story: Push them to test, explore, whatever until they figure out what is going on with you. Unfortunately it seems this stuff can, and does, happen out of the blue, and is not age discriminatory.