It's never happen too me, I'm pregnant with my first...but it may come up negative if your hcg hormones are low. Try and retest again in a week
With my second, I used EPT pregnancy tests, they never read my pregnancy. I had an extra test left over and just for fin took it at like 4 1/2 mos prego and it was false. I'm pregnant now with number three and tested positive the day after my period was epected with the clear blue easy digital test