When to take pregnancy test?

This is our first month trying. I believe I ovulated between the 11th and 13th. When would be the earliest I can take a pregnancy test? I used an OPK on the 11th and it was almost positive. Took an OPK on the 12th in the morning it was also almost positive and again on the 13th and it was negative. I believe I surged on the 12th and had spotting on the 15th.