Is diarrhea a symptom of pregnancy?

I have been having diarrhea on and off ever since right around the time I likely conceive. My stomach is just super sensitive now it seems. I had constipation with my first pregnancy so this is new to me. I went into the doctor and had blood work and a stool sample taken and everything was normal and showed no sign of infection. I'm right around 5 weeks and this has been going on for about 3 weeks. It's not fun! Anyone else experience this? The doctors won't say it's from the pregnancy but they won't say it's not either.