@Steverpeeps , you said you think it’s something scary. Are you worried about anything specific, other than ectopic? How old are you?
Ovarian cysts can be quite painful sometimes, but they are not dangerous. Fibroids also are not dangerous, aren’t common in young women I’m making an assumption here and wouldn’t explain the late period and hormonal symptoms.
Another possibility to consider as a GYN cause for one sided pain would be a PID pelvic infection that is localized to one tube, but again that wouldn’t explain the missed period and other symptoms.
Are you using a birth control method? If not, do you want to be pregnant? If not, maybe this is a good time to get started on reliable birth control. If it is an ovarian cyst, starting the depo shot or the pill would help it get it started toward going away. And then you wouldn’t have to go through this worry again.