Late period but negative pregnancy tests

My cycle is usually 28 days. I am now four days late, but two home pregnancy tests that I took were negative. What could be affecting my cycle? I am taking Prednisone for hives, but I read that it is rare for Prednisone to affect your cycle. Any ideas? I really am hoping that I'm not pregnant, and now I'm freaking out because my period is late! Could two pregnancy tests be wrong?

[Kimberlee_20]

If you were pregnant a positive HPT should be showing by now, though some women it takes a little longer. Any new medicine to your body can throw your cycle out of wack, so it very well could be that, even if it's rare. You're probably not pregnant if you're still getting negative HPT's, wait and see if you get your period, if you don't, test again next week sometime with first morning urine and contact your OB/GYN. Good luck!