Period 4 days late but definitely not pregnant, why would this be?

[Lsquiggles]

My periods are always very regular and happen on the day they're due or a day after. I'm now 4 days late and worried as this has never happened before! I'm definitely not pregnant as I've not had sex.

I'm not overly stressed, I'm mid twenties, haven't gained or lost weight recently. I had gallbladder surgery on October 26th, could this impact my periods?

Bump

I've had this happen to me occasionally over the years. I've never worked out what causes it, but it's always gone back to normal the following month.

Did you just skip a period for one month or did your period eventually turn up after many days?

Probably stress related. You do come across as quite anxious atm.
I think it happens to all females at some point in their lives.

Mine eventually turns up, I've never skipped a cycle.