Clinical guard tests

So I took a test this morning. It is Clinical Guard test strips that I bought on Amazon. And this line appeared in 5 minutes. It got me really excited so I tested again on several different kinds of tests. But everything after was negative. Because of how faint the line is, I kinda expected that. But I figured I might see some sort of vvvfl on at least one of the other tests. But nothing. I've been using these tests for a while and I've never had a hint of a second line until this one. I'm going crazy. I'm going to keep testing and hope the lines get darker. But until I have a clear second line, I'm keeping from my DH. Anyone have a similar experience?