Sex after IUD

So I'm starting to get extremely worried, my boyfriend of 5 years and I never use condoms and haven't ever in the past. We have both been tested for stds recently and both of us were negative. I recently got the IUD put in and ever since then, when he comes in me, my vagina becomes extremely itchy! It lasts for a few days after we have sex and is almost so unbrarable I can not leave my house. This had never happened before the IUD was placed and I know it's not an std or yeast infection. If anyone has had any experience, has any advice, or any ideas of what could be the problem, PLEASE HELP!