I'm 16days late on my period but showing negative test could I be pregnant? I'm always tired sleeping a lot, get full from food quite quick!etc

It shouldn't be that you're pregnant. You may be going under pressure it happens. When we girls are under pressure our hormone system becomes messy.. maybe you're sad or need some pace for yourself.. did you have sex recently without protection? If yes then you might need to go see a doctor to make sure it's not pregnancy or if it is.