Need advice

Cheyanne

My last period was on 4-27-18, I ovulated on 5-10-18. I was supposed to start my period 5-22-18. I didn’t. Starting on 5-25-18 I started bleeding, which I thought was implantation bleeding even though it was a little later then expected. It’s a light pink and light spotting. Anyway it lasted 1 1/2 days, then just stopped. I took a pregnancy test last night it said not pregnant, when should I test to be able to get a correct positive or negative. Today is 16 dpo.