You are not alone. I work in a school with plenty of female teachers. We have a faculty only bathroom with 3 stalls. That doesn't always mean that no students will come in. If I go in and someone else is in the bathroom I will try to hold it until they flush or turn the water on or leave. With teachers in classes it is pretty easy to catch the bathroom with no one in it.
I hate when someone wants to chat with me especially if I am having stomach cramps. I have been on my way to the bathroom and seen a teacher go in and I have headed to another one to hopefully catch some privacy.
I guess it all boils down to everyone poops and we shouldn't be embarrassed but it is hard not to be.