So
Here, I thought of a way to answer this as I do not think lying is healthy.
There are ways to redirect, and be honest without showing someone your skelleton.
Skillful means.
I would probably say:
"oh, no, sorry, I have a really irregular period. I just have some hormone issues. I have been seeing a doctor about it." and to ellaborate " I've had some stuff go on for a long time."
There. That way you are not lying, you DO have an irregular (as innot regular period [it doesn't exist after all, very un-regular]) you are not on your period, but it is honest, and helps explain why it might come up again.
That way they actually feel for you, provides an honest(but not full) explaination of why you might take homones if they see you-"my doctor thinks it will help my hormone issues."
Honest, easy, redirected. No Lying, just skillful redirection. Some Verbal Aikido.
That's my suggestion