There are different cysts, most common is fluid filled. Which generally do burst after menstruation begins. But for a cyst you would generally have pain in the lower right or lower left abdomen. But you state pain in the lower middle. Which then would indicate PID. If you are having any pressure or problem with urination, then this would indicate UTI. If you are having none, and the pain is in the middle, chances are this is related to PID.
I would still make an appt. And ask them to please call you, if they have a cancellation. If it gets too severe, I would be seen in the ER. You can also worry about billing later. But the ER would have to treat you.
I am also going to give you a link for appendix problems, just in case the location of the pain shifts. Appendicitis
Hope this helps Hun.