pregnancy symptoms?

A few weeks ago I had sex with a Condom when on the placebo week on a Saturday (period had finished) I have always taken my pills on time and never missed one, my partner always wears a condom but we usually check and wasn't broken! 
By the Wednesday I started feeling nauseous and feel pressure in my lower pelvic area as well as frequent urination, this pain is still continuing. I took a test and it was negative and got my period.  
How early can you experience pregnancy symptoms? I'm not worried, I'm just curious how early.... 
This question sounds so stupid, it's embarrassing considering considering I'm plenty old enough and married!