Why would I have a 16 day cycle??

[Largemelons]

Af just arrived 16 days after my last one!
I'm not on any contraception, not pregnant and my cycles are pretty regular but can be anything from 21-27 days.
Last af was pretty light but a definite period as sometimes they are light.
Any oracles out there?
I'm 36 with 5DC.

Cycles shorten as menopause approaches but any less than 20 days should be checked by a doctor. Are you sure it wasn't a breakthrough bleed?

I'm 40 and have a a few cycles between 12-19 days over the past 2-3 years.....perimenopause I'm afraid.

Nooo! I'm too young for perimenopause!
What's a breakthrough bleed?

Btw I haven't had sex since last period so can't be implantation

Breakthrough bleeding is any kind of mid cycle bleeding and can be caused by lots of things. Being on the pill is one.
Was it a normal heavy period or just light spotting?

It's still going on, quite light but I'm very crampy.
I'll try and get a GP appt next week and get my hormones checked out.
We're not actively ttc but if it happens then neither of us would mind. After years on hormonal contraceptives I decided last year to get the implant removed. I had an early mc over a year ago but nothing since although we generally avoid my most fertile times.

Maybe you're still readjusting after coming off long term hormonal contraception? Good plan to get checked out. If you're GP offers hormonal blood tests make sure she/he gets your blood tests between day 2-5 of your cycle otherwise they're meaningless, (mine didn't realise this, but my consultant pointed it out)
and get LH, FSH, thyroid and Estradiol levels checked.