False negative????

So I'm 11-13 DPO and I have had symptoms I never have: sore breasts, nausea, fatigue, a little cramping for a few days and now it's gone, a few spots of brown blood in my underwear (sorry TMI) but I took a test (not FMU) and it was negative, I could swear I saw a faint line but I probably just have line eyes. I'm still 3-4 days from AF but I took a test anyway. If I got a negative could it just be due to testing too early or not using FMU?