Has this happened to anyone else

This was the first month I used opk tests and found peak ovulation was Tuesday, April 17. Dtd a few times in fertile period. Friday, April 20 I started spotting very light at first. Then nothing. As the day progressed was a little more. Just needed a panty liner so not heavy. This morning when I woke up there was nothing but throughout today brown just when I wiped. And now nothing. I had one opk test left and it came back w a strong positive today. How is that possible? I’ve heard an opk test can detect hcg levels. Should I take a pregnancy test? Not supposed to start for 9 days