If you've been trying to get pregnant, perhaps your suspected AF was actually breakthrough bleeding and the "period" at 11 days was a chemical pregnancy? Whatever it was, I would bring up to your doctor, but I wouldn't necessarily be concerned until you have more information.

It's not a problem for cycles to vary a lot in length, but your luteal phase (post-ovulation to AF) should stay constant. One option is to not just take OPK's, but to actually chart. Check your cervical mucus earlier in your cycle (when you're not using OPKs/days you're not having sex) and to temp (confirm ovulation). With better records, you'll be able to tell what part of your cycle is changing and better hone in on the problem with your doctor.

did you ovulate during this 11 day cycle? i'm guessing you didn't and it's not an actual cycle -- that your previous period was "breakthrough bleeding." another option is that your previous period was ovulation or implantation bleeding and you're actually pregnant.

just as fyi -- my cycles were also quite regular when i was trying (have 2 month old now). the month i ended up getting pregnant i didn't ovulate when expected. it was my first month temping, so i was super worried that i wasn't ovulating at all. i just kept temping and doing OPK's and ended up ovulated two weeks after i would have expected my period based on cycle length. then i ended up getting pregnant when i did ovulate. (and good thing i was temping, too -- otherwise we would have been really worried when baby looked so small on ultrasounds compared to LMP).

anyway, are you sure you ovulated on day 16 or 17 this last time? if so, i'd take a pregnancy test.

the other thing is that cycles do get messed up as you age. also if you were stressed (or not eating well, or exercising too much, or sick...) during ovulation.

I am 34 (almost 35) and have been actively TTC for 6+ months for the first time but was having unprotected sex before that. I have been temping and charting since April and cycle has been 29 days with ovulation on day 16 or 17 every single month (confirmed with OPKs). My periods have been like clockwork for the last two decades, and yet today I got AF only 11 days after my last one and it's not just spotting. I have never been on BCP and I can't think of any other factors that could have triggered such a short cycle. I got the day 3 testing from the OBGYN and everything was normal, although I know there could be other things going on and I plan to make an appointment with an RE after I turn 35 in a few months. Needless to say, I'm stressed out about what this could mean as well as having yet another month of failure without even getting a chance to try. I'm also unsure where to go from here and am thinking I need to use OPKs more frequently and outside the usual window if my cycles are irregular. Any insight into why this happened? I understand it could be just a one-time thing but I want to make sure I'm not missing something.