am I or aren't I?

so I had the copper non-hormonal IUD removed on August 7th..was told I could get pregnant immediately..we have been actively trying since that day...I should have ovulated that week and since last Tuesday I have had many pregnancy symptoms..nausea, food aversion, headaches, increased sense of smell...my period is 2 days late but 2 pregnancy tests came back negative...is it possible to be pregnant and test negative...its been 15 days since the first day we could have conceived????