IUI and pregnancy test

I had my second IUI on 2/4. Period expected 2/18. I took a test on Monday and I thought I saw a vvfl then I took another today and it was negative. Anyone else have seen this before? Is it still to early to test? They told me to test Saturday but I can't wait. What are your most reliable tests? Thanks for your help ladies. It's been almost 2.5 years of trying and I'm just feeling defeated.