Confused by digital tests

I am trying to conceive baby #2 with irregular periods so I got the digital ovulation tests. It was negative on Sunday, positive on Monday and negative again today. I thought it was supposed to tell you your 2 most fertile days? Even if I am negative today... can I still get pregnant if we have six today? A little confused! Thanks for any explanation!

P.S. I took the strip tests as well and got the same results FYI