Urgent advice required please!

Ok so long story short, I had the mirena coil removed due to health issues, and replaced it with cerazette mini pill, which has been missed a couple of times, (bad on my part but genuinely had mind else where) anyway I'm not due my period until next week however yesterday and today I am spotting brown discharge and last night was about a teaspoonful of red blood but now it's back to the brown discharge, not a lot just medium amount, I have tender breasts and I'm sooooooo tired, I did a test yesterday to rule that out and it came back negative, could it be possible and/or too early? What is going on with my body?!?! Feeling so fed up with it right now!!