New to Glow - positive OPK negative HPT...

Rebecca
Hi all, am 9dpo. For some reason (what goes on in a womans mind?!) did an opk yesterday at 3pm it was positive then again at 10pm and again positive, so purchased a clearblue digi this morning but its negative. Could I be ovulating late? Or can opk pick up HCG levels before a hpt? AF due Sat 26th July.