How often are tests wrong?

Stephanie

I've been feeling sick since last Friday. Sick as in cramps but they're not cramps, nausea, headache and swollen feet-add in I wear a size 9.5 and could barely fit into an 11!!! A friend of mine said those are all pregnancy related but when I took the test it was negative.

I'm about a week away from my next period but my last was was about 10x lighter than my normal super heavy ones. Anyone else have similar issues or any insight?