What Causes Delay In Periods, Brown Spotting And Bright Yellow Urine?

Hi, my period was due on the 15th march, last period started on 15th feb and lasted 7 days, which is normal for me. This month period has not arrived its 30th march, and ive had brown/blood streaked spotting discharge for about 2 days. Ive done 3 home pregnancy tests which have all been negative. Also i have noticed my urine is bright yellow(if that could be anything to do with it) What could be going on?