Tess, did you do another test or two today? Don't despair, if you are one of us that has a hard time getting a true positive then you may need to test more frequently (I do!).
To check weather you have ovulated you could go to your gp and get a cd21progesterone level done. This is a blood test and it will confirm ovulation. Progesterone levels peak 5-7 days (or thereabouts) prior to when your next period is due.