Did my ovulation date change?

My original ovulation date was set for 1/27 and opk was negative/very faint lines. Now I got 2 positives today and says I'm supposed to ovulate tomorrow and my period date changed. My period arrives every 28 days on the dot so it just seems really odd, and my opks from last month were right on schedule.

It's our first month trying and had planned to BD yesterday through 1 DPO. I planned to test again later today before we BD to see if it's still peaked but my period is literally always the same so I'm confused on these test results and potential date changes.

Can your ovulation date change, or could having sex give a false positive opk?

If it can change and affects my period due date, how soon should I start pregnancy tests?