I echo HVAC's comments.
Another possibility / explanation for this pain could be endometriosis. Endometriosis implants / lesions typically cannot be seen on imaging. It is possible that this cyst is an endometrioma which is associated with endometriosis. Also, endometriosis tends to run in families. Some women undergo hysterectomy and ovary removal as a "treatment" but, unfortunately, that is not a cure so may not relieve the pain especially in the long-term. And then they are left with the medically documented negative health and quality of life consequences of losing the lifelong functions of these vital organs.
The fluid in your pelvis may be an indication that this cyst is leaking or you had another cyst that ruptured which can be quite painful. It can also cause an infection, which may also explain the pain.
Seeing your gynecologist for a follow-up ultrasound seems like a good plan. You don't want too many CT scans since those emit a fairly high dose of radiation. Let us know what you find out.
Unless you have Ovarian cancer specifically in your family or have the BRCA mutation you have 1.4% chance of Ovarian Cancer in a life time. I think your plan is a good one since Ovarian cancer gets missed. Most cysts are benign and some can cause pain and discomfort. Let us hope yours is benign.
Alex
I should also mention, I'm in my early 20s. My grandma and aunt both had full hysterectomies in their 20s because of tumors. Problems run in the family with the female organs.