no period?

I was suposed to have my period,on the 2nd, it didnt come. today the 4th I woke up with brown discharge and slight cramping. I have been trying to get pregnant. I have a 30 day cycle spot on every month my period comes the exact day it should and normally it starts light pink not brown. so my question is has anyone ever experienced having some brown discharge while pregnant when they would have had a period if they were not pregnant ?? I hope that makes sense.