Lately I've been a little bit suspicious of something else, too. I know Sage eats a lot of hay each day, so it's no surprise that she has developed quite a belly. However, it's always a possibility that she was bred by a stallion while still out on the range...meaning, at the least she could be 5 months pregnant right now.
Teen pregnancy? Well, she was a big girl for 2 so it wouldn't be so out of the question. I may just be paranoid, but maybe when school starts up again I'll get her tested.