What Causes Vaginal Bleeding After Intercourse While On Implant?

hi i am a 26 yr old mum of 3 and breast fed all my kids for a yr each. I have had implant in for 7 months. I had no bleeding for the 1st 6 months but may had what i would call light period for 4 days every 2 weeks. The problem is since having these light periods,for the last two times i have had sex i have bled after. No pain just blood this has never happened before. The 1st time the sex brought on my period but last night was just light bleeding.