First month of using OPK strips. Started on CD10 and it was negative. Got home from work late CD11 & didn't test. Tested today CD12 and got a positive (not heavy or faint more a medium coloured line I would say). Had already did the BD before I tested tonight. I tend to drink a lot of water throughout the day (around 2 - 3 litres) so thought testing around 7 or 8pm would be best. So going to test again over next few days as mycycle.com estimates I will ovulate around CD17 (periods have varied in length). Tummy is a little sore this evening (currently sitting with a hot water bottle on it). Any advice ladies?