What Causes Delayed Periods Along With Vaginal Spotting?

Am I pregnant? I ve took two pregnancy test but they both came out negative. My period was suppose to start February 16th but it s already the 28th and nothing. My period doesn t always have the same cycle the dates change a lot. I weigh 165 lbs so would it just be other problems? I have no early pregnancy symptoms and I ve been really stressed out more than usual so could it be that too? Since yesterday I got a bit of blood I thought it was my period but then it stopped. Today in the morning I got a little bit of more but my urine was still clear a bit. Right now I got more blood and my urine was red it had a bit of clots when I wiped so could it mean my period is coming? I also started exercising so I heard that it could make your period late as well. Please respond thanks