Confused...

Georgia • Single. Tiktok video maker. Stress head.
So my partner and I have been trying to get pregnant (not a very long time I'll admit, maybe like 3-4 months) and recently I've been experiencing something strange. I'm almost two weeks late for my period and I've felt nauseous so we decided to do a test but that came up negative... I have very regular periods maybe only been a day or two late before and I've not been anywhere near as stressed as I normally am from my job and other stresses... 
So pretty much I'm just confused as hell why I'm late and nauseous but the test has come up negative