too soon to test?

So I had unprotected sex on the 26th, took plan b on the 27th. I was scared about pregnancy so I've taken two tests. One on the 10th and one today. Both were negative  but I'm using the first response know 6 days sooner thing. My period is supposed to be due in 6 days. Is it still too soon? I'm pretty sure they're going to keep being negative but I don't know.