Give it a few days and if you still don't have a period then take another test. The sensitivity depends on the brand you are using, I found first response to be sensitive enough to use 2 days before my period to get a positive. Also the chances of a positive will be determined on the HCG levels in your body (if any) which can vary a lot from woman to woman in early pregnancy. Your not overreacting, its best to be safe and check, assuming you were on the pill, best not to take it until you know for sure your result, just use condoms etc. until its ok for you to go back on.
