I haven't had a singleton pregnancy, but I'm going to comment anyway!
I felt err ... swollen ... from about 11 weeks with my twin pregnancy. GP tested me for everything and came to the conclusion it was just the weight of the pregnancy on my pelvic floor muscles. Then we found out it was a twin pregnancy
For what it's worth, my pelvic floor is as good as before now! I did have an ELCS though, which probably spared it too much damage.