Af due tomorrow, light brown spotting

I am due tomorrow. Today I have had a small amount of light brown spotting, no red at all .

I've had nausea and extremely sore boobs for about 5 days and a metallic taste in my mouth.

I haven't tested yet but I'm not sure if this is af or something else.

My boobs feel exactly like when I was pregnant in august

Any ideas of what this might be?