Implantations dip...how accurate?

I had a dip at 7dpo. My chart is only my LP because I wasn't sure we would TTC this month after a chemical. Anyways, I started right after ovulation. Here is my chart. I don't feel pregnant at all. In fact, I feel like my period is going to come early. AF cramps and backache since 4dpo, and cm is scant. My boobs are sore, but they always are. My hopes aren't up, but I'm just wondering how often this happens?

Past this, I only charted once and it was when I got pregnant last time. My chart did not look like this though.