Ammonia smelling urine

It seems pretty common that I get a strong smell to my pee before my period, and I've never really known why. But, I'm 9dpo with AF expected to be here on Tuesday. Since I don't know what causes the ammonia smell, I didn't know if it's associated with period or not... meaning, if I am smelling it does it mean that I am going to start my period or is there a chance I could still be pregnant?