What kind of cyst is filled with blood, and what are the consequences? Do I have endometriosis?

I was told I have a 4 centimeter blood-filled cyst. What kind of cyst could it be?

I had an IUD for 5 years since I was 19 because I couldn't tolerate the side-effects of birth control pills. My periods were heavy and I immediately had terrible cramps and pain before and during mensturation, but I assumed it was normal with an IUD. I began noticing especially sharp unbearable pains when I was on the heaviest days of my period and had to pass gas or a bowel movement. These sharp pains usually lasted only a couple seconds during general painful cramping.

In February (i'm now 24), I began getting usual cramps, andthe sharp shooting pains, but instead of lasting seconds at a time, it plateaued and lasted for almost a whole hour. The pain was excruciating, I had to call 911 but was in so much pain I couldn't even talk to the operator. At the hospital they took out my IUD and tested me for STDs and PID, but everything was fine. I was treated for PID anyway "just in case". I had an ultrasound and several cysts were found. A month later, another ultrasound revealed the cysts had resolved themselves except for 1 that was 4 centimeters big on my left ovary. An MRI showed it was filled with blood, says the doctor. A few months later I had anoher episode of pain, though not nearly as bad, it left me with difficulty walking for days because it was still sore. 6 months later I've had another MRI. I get the resuls tomorrow.

Is a 4cm blood-filled cyst endometrioma? Does it sound like I have endometriosis? Is that why I have cramps? Or was in the IUD? Could I just have a large functional cyst that was filled with blood? What is the "fluid" that supposedly filled a functional cyst?

Could the extreme pain I had been from torsion or rupture? What if the cyst is not gone, will I need surgery? For a 4cm cyst, would I need open surgery?

What is the impact on my fertility? I am about to turn 25, but do not want to have children until my mid30s.