cramping and bleeding after sex???

My SO and I have been together for almost 4 years. Lately (ever since I got my IUD), I've been bleeding after sex! Not heavy but very light, I'll see it when I wipe. But tonight, I was actually very wet until the last minute that we had sex (that's when we noticed I got dry), and when I went to the restroom and came back to lay down I started cramping really bad after. I'm just confused because before during our relationship, we've had rough sex to where I'm not fully turned on and I wouldn't bleed either way. I wonder if this could be a side effect to the IUD?