I'm late but still getting a negative test.

MJ • Married 5.25.13 💍💙 Expecting baby #1 September 5th 2018 🤰🏼

I'm three days almost four late for my period. I've never been this late ever so I took a pregnancy test this afternoon (after drinking quite a bit of water) and it came out negative. I've had no signs of a period but have been struggling with headache and some constipation. Is this normal? So frustrating!!!