What Causes Bright Red Vaginal Bleeding After Having Sex While On Implanon?

hi, i've been on implanon for four months now with irregular bleeding which i know is normal but for the past two weeks, when my husband and I have sex I have bright red bleeding afterwards which just lasts about 2hrs, I also experience a cramp on my left side of the abdomen, is this normal and due to implanon or serious to get checked out by my doctor?