Help please

I have been trying with my husband for number four for 5 months it has never taken this long with any of the others! Well today my period was suppose to come and didn't and I've been constipated and nauseous but I tested on Saturday and it was negative! Any thoughts???? Is glow pretty accurate with your periods and is it normal to take this long when it's been quick with the other??? I'm getting discouraged! Should I test again?