What Causes Delayed Menstruation With Negative Pregnancy Test?

Hello, I am 3-4 days late for my period (CD37) and spotted twice this month. Both times the discharge was light pink and only last a day or two. I have never spotted in my life before. Over the course of the last week, I ve also had to deal with terrible cramps. I also have several new pimples, which is bizarre, as I haven t had any since I was a teenager. I am nearing 30. I took 3 home pregnancy tests (twice before my period was due and once this morning), but they all came back negative. What is happening to my body? Any help would be most appreciated.