What Causes Discomfort In Having Sex?

I had a total disc replacement at L4/L5 and a fusion at L5/S1 three months ago. When my husband and I had sex for the first time 8 weeks post-surgery, my anatomy was different - he no longer "fit" the same way and could feel the angle of my tailbone preventing him from normal intercourse, and I could definitely feel the difference. It's enough to make sex uncomfortable for both of us. What could this be? My doctors don't seem to have any good answers for me, but there must be some explanation, and something that can be done about it.