Ovulation and cramps on the nexaplanon!

Hello, I am 10 months post partum, I had my baby girl last year. I had the implant fitted two months after birth, since having it in, I have ovulated a couple of times over the months. This week I noticed I had ovulated (cm) day after I had stomach cramps, these cramps have been continuing, also I have been getting back cramps. I know the implant is 99.9% effective but I thought it was impossible for you to ovulate. This is my second implant and the last time I never had ovulation ect. I took a test (obviously way to early) it was negative. Also I've been getting movement in my stomach. I've not got a question to ask really just has anyone been through this?