Stopped BC and period is 22 days late,

The title says it all...I stopped The Nuvaring last month and my period is 22 days late so I obviously took a test, 3 actually and they were all negative...I already have two children and urine tests worked to tell me I was pregnant with both of them...what could be going on besides pregnancy??? Oh and my obgyns nurse kept insisting on the phone that "you're probably pregnant so you need to come take a blood test" as if there is no other reason for my late period?