Birth Control

So last month I started back on the pull after a couple of years. I ordered from Nurx and got my pills in 2 days after my period and started them immediately as my doctor said I should. She told me to wait at least a week before unprotected sex and I waited ten days. When it came time for my period I never got it. It’s now 16 days late. I took two test that both say negative but I’m paranoid and afraid that I am. Has anyone else experienced this or know if it’s normal?