need advise please

We have been trying for about 6 months now after having a miscarriage the first time. I have been taking a fertility supplement for the last month to help us. I normally have a regular period the app is usually spot on for the day I am suppose to start. I am now about 4 days late but the rest still came back negative. The only new factor is the fertility supplement so could that cause me to miss a period, or give a false negative? I don't know what to think or do please help me