Feels like........

I'm going to have diarrhea, but everytime I go try to do anything there's nothing. This keeps happening on and off though out the day just not every day. It's getting annoying. I'm 34 weeks pregnant now and chase my 2 year old around the house all day. Why does this thus feeling of like I'm going to crap all over keep coming and going. This never happened with my first pregnancy.