Period late, weird symptoms but negative test - could it be false?

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Hello, I'm 38 and been TTC for a few months (after first child born in 2017).

I use an app to track my cycle and it's usually roughly 26 days, although often varies by a day or two. Now on day 30 and no sign of AF at all. This is different to recent months, as I usually get spotting a few days before. However, I've had some digestive weirdness and generally feel a bit strange... could be hormone-related?

Took a test yesterday (cheap strip type - don't want to waste the posh ones yet!) and it was DEFINITELY negative - no sign at all of a second line.

So... do you think it's just my cycle being weird? Or is there any possibility of pregnancy, but HCG levels aren't high enough yet?

I've been quite stressed this month, so I didn't think there was any chance of success (and it's another reason my period could be late). Because of my age, I'm super-paranoid about fertility :(

However, I had an LH surge around the expected time (positive OPK).

If anyone can offer any advice/opinions, I'd be very grateful.

If you can, try continuing dtd every other day in the week after you SMEP. It's tiring and can be less fun but still, needs must!

Do you get any ovulation pain at all? Mild cramps, usually in the right hand side?

@YoBeaches - Not that I recorded (I use the 'Clue' app). I've sometimes felt what may be ovulation pain, but it varies... and I've been doing a lot of heavy-duty gardening recently, so I have a lot of muscle twinges in my core! Just to confuse things further...! Thanks again for your input :)

UPDATE: I had some light spotting yesterday and continuing today, so AF may finally be here. If it does appear this week, it's approximately 2 weeks since the EWCM, which would make sense.

Summary of late period issues while TTC

Just for future people with the same problem, this is what I think happened to me, during the last cycle (it's really freaked me out, over the last week):

Day 14: LH surge (positive OPK), bang on schedule.
Day 14: Also a really stressful work event, which affected me all week.

Day 15: I assumed I ovulated - but I now think it didn't happen, due to the afore-mentioned stress.

Day 25 (possibly also days either side): Random EWCM - I didn't test, but if I had, may well have seen a second LH surge. I now reckon this was when I actually ovulated (my body having a 'second go').

Day 26: When my period would usually start (ish).

Day 35: Spotting and general AF symptoms - so when it appears properly, it's likely to be about 2 weeks after that random EWCM, which would make sense for the ovulation/period relationship.

Unfortunately, by day 25 we'd stopped DTD! So next month we'll probably carry on with every other day...