I’ve had 3 babies and have never had this happen... plz help!

DH and I have 3 healthy amazing kids, ages 8, 5, and 14 mo. We are on the fence about #4 and are rolling the dice... just having sex when we want and letting fate decide. But I’m doing OPKs to have some intel into pregnancy likelihood.

So. I got a fairly negative (not invisible but not dark) OPK the day he got home from a business trip. We had sex that night. Got a clear positive OPK the next day along with obvious ovulation cramping (on the right side only, intermittent sharp pain), and haven’t had sex since. Now, I’m 5DPO and having very light brown-red spotting...very very light...

Does this sound like implantation to you?? This have never happened before.

TIA!!