So, how (for example, hypothetically speaking ) have just come off contraception and haven't had a period yet, how could I date my pregnancy?

I think I know when I ovulated (16th of Jan) from my symptoms and I may have had something som spotting on 25/26 Jan. But I don't know my cycle length!?!?

We are using condoms , so I'd be very suprised if I am pregnant but I'm just wondering...

TIA for your help!