Is it possible for a female to be pregnant while still having regular periods given that she is on no drugs or medication.

I always thought no, but I've recently heard of one or two instances where it's happened.

possible yes but about as rare as a ginger boy getting laid.

There would have to be some serious fuckups with the hormone levels for anything like that to happen...

I don't know whether it's possible, but it's certainly not likely.