missed period on birth control 4 negative tests

I have been taking Losterin 24 for about 7 months now and i recently missed a day and when i relized it i took the pill and then i was late a couple of days later about 4 or five hours late and i had spotting like my period then when it came time for my period it didnt come i have taken 4 pregancy tests since then and it has been three weeks since the first test and all have come out negative should i be worried i have had some headaches and stomach aces but nothing else

should i be worried