Call a dr?

I was supposed to start my period in Tuesday (the 4th) and it still hasn't came. I took a pregnancy test on Monday and again yesterday (the 5th) and ate coming back negative.

When is best to call a dr? My period normally lasts from Tuesday to Friday/Saturday and I have had only some cramps for symptoms of a period and that was on Tuesday when I thought it would start. My period is very regular so I'm concerned that something else may be wrong if I'm not getting a period and getting a negative result for a pregnancy test.