Ovulation tests

1st time using ovulation tests an I started using them the day after my period because I had suspicions that I ovulate earlier than my app suggests. Turns out I had a positive test on day 6 after period ended. Me and my partner missed that day sex wise and ever since iv been having negative tests. Is it right only getting a positive test for one day? I was under the assumption of still getting positives for at least 36hrs after the 1st positive. I'm really confused and upset iv missed it. Someone please help me understand.