What Causes Stomach Pain And Mood Swings While Using Birth Control Implants?

Iv just had a baby nearly 7 month ago. I have the implant put in 8 weeks later. Ive been having very sore stomach aches like a shooting pain,my periods are all over the place and im having terrible mood swings. My stomach is very hard and has been for weeks. Do you know why im getting any of these? I thought the mood swings from the implant but didnt think from any of the other things i am getting.