best days to have sex

So I have been using the clear blue digital ovulation tests. Have been testing for several days but Monday morning and night no surge, had sex. Tuesday morning tested positive for a surge with a happy face, had sex at night. This morning it tested no surge but the glow app is telling me that I'm ovulating and we should do it again Tonight, is this true? I'm so confused! When is it past the point of possible conception?