I think I’m out this month

I’m 16 dpo and I am still getting negative tests. I ovulated on August 30th which was verified by my doctor. We had sex on August 29th and twice on August 30th and twice on August 31st. I started cramping off and on at 8dpo which I thought was implantation cramps but I guess not. We want another baby so bad. My period is three days late. Last month my period was ten days late. I’m feeling like my body is failing at the one thing it was made to do. Has anyone gotten a BFN at 16dpo and gone on to get a BFP later?