I've experienced that long before I even thought of taking T. It's probably caused because during sexual arousal the uterus changes position slightly, and in order to do it, it uses several muscles inside of and outside of itself.
Personally I'd say the FTM equivalent of "blue balls" is the irritating ache sensation much closer to the outside genitalia and in the V that you can get just by thinking about something but not acting on it at all. Probably caused by the blood vessels dilating in the area.
For me just the thought of all those damnable female organs moving around wanting to fulfil their female functions generally just turns me off. I don't have much dysphoria regards what's "not there" on the outside but those inside bits can forget ever fulfilling anything.
