Stop punting and go to the Sexual Health Clinic and get tested.
You had unprotected vaginal sex with a complete stranger, trusted her certificate that was 20 days old and her word that she hadn't taken any risks since. Whilst you may not be showing any symptoms you could still be infected.
And if you had any unprotected sex with the SPs you have seen since then it would be courteous to tell them if your results come in positive.
