Very confused! In need of some help!

So I was 3 days late for my period and I was a little worried so I waited to see if I would get it. I ended up starting to spot which was very unusual because my flow is always consistent and always heavy. I had no early period symptoms which I always get the week prior to my monthly. I took a test and it came up negative, so I assumed it was an irregular period even though its never happened to me before. Its been less than a week and Im still only spotting. and it went from pink to brown. I have taken two more test and they still came up negative. I've been feeling very tired lately, i have had a headache for two days as well as nausea and tender breasts. I'm very nervous to know if I'm really pregnant or not. Usually if I think I am I take a test and if it comes up negative I get my period the day after with a heavy flow, excruciating cramps and nausea. I was just hoping someone could help me understand what could be going on with my body!! or if anyone has ever experienced my symptoms