Hi Suz,
You should have a brochure with your tests that tells you when the optimal time in your cycle to begin testing is. EWCM often happens for a number of days and it is generally thought that you ovulate on the last day of this mucous. So, I would continue testing and also get jiggy with it too! You don't want to miss that egg when it hatches! It is possible that you are say ovulating today and therefore you would have probably received a positive opk yesterday. Conversly it's possible that you will ovulate on Sunday and get a positive opk tomorrow. So, keep testing. What Cycle day are you on? How long was your last cycle? Good luck!