Worrying - 4 days missed

I have missed my period by 4 days. I have had all the usual symptoms come like sore chest, mood wings, little cramps but nothing has happened. I took a test today and it came back negative. I’m worried as if it’s not pregnancy, it could be something worse. I haven’t changed any habits, my cycle is spot on all the time. I’m not sure why this has happened. Was it too soon for a test? My chest hurts so much more than what is usually does. I have on and off tiny little cramp like pains but nothing is happening! Any explanations? Thankyou!