Implantation or start of period?


I had a miscarriage on the 23rd April, stopped bleeding on the 27th April. I ovulated on the 7th May and also had sex on the same day and the past 2 days I've had back ache but today the ache has been worse and had a few stomach cramps throughout the day aswell. Could this be implantation bleeding as it was 13 days ago and fits in the timeframe for it or could it be the start of my first period after the miscarriage?