I would test (early as it may be) incase you're pregnant from your previous cycle(s). I'd then test every 4-5days until my next bleed, JIC.

I didn't know I was pregnant with my DS until towards the end of the first trimester! Needless to say my reaction was far from ideal, his conception wasn't planned and came at a cross roads in our relationship. We also had a 6month old DD. All the symptoms I had with the twins (DS was a single born live baby in the end, I miscarried his twin) I ignored because I still had a 'period' and never took notice of the symptoms. Like Limeslice said, hindsight is great.

Sometimes our imagination and fears can let us get worried, but to be sure, test-there's nothing more positive or negative than a decent POAS.
I hope that the results are what you wished for, and if not, what will be will be. xx