Period due December 31st

Hello so since about summer my boyfriend and I haven’t “prevented” pregnancy - we didn’t track it or anything. December was the first month we actually decided to just try 100% ! I have been tracking my period with this app for a full year now and my periods have been on point within a day of this app until December ! December 31st was the start date so I waited until January 3rd and took a test (negative) so I figured I would start anytime now but I haven’t ! Nothing has changed lifestyle wise and I haven’t taken another ! Someone told me that I could ovulate later in the cycle making me have a false negative ... anyone have experience with this ? I plan to test again in a couple days but if negative would you see a doctor or just wait ? Would I still ovulate like normal ? I have no symptoms of a period starting (my breast usually swell and hurt) nor any “pregnancy” symptoms - only thing I’ve noticed was mild cramping so I thought I was going to start but nothing ! Any help would be great :) and thanks again !