Period late. Pregnancy test negative

Just wondering if anyone has experienced a four day late period. I did a pregnancy test after the first day I missed my period and then again today (4 days late). I’m not under unusual stress or have lost significant amounts of weight. I’ve just been really happy lately and can not figure out what’s going on. Any suggestions? I’m just really frustrated that neither my period has started and with negative tests. Also worth noting my period runs like clockwork! I’ve never been this late, at least not for a number of years and not on birth control.

My cycle runs 28 days, had unprotected sex a day before and a day after ovulation (cycle day 14 and 16). No plan b. Currently on cycle day 32. Thanks!