I am 15 weeks pregnant had been having diaheria then was constipated now there is white stuff in my stool what could it be?

Sounds like yeast: Yeast infection of the bowel is very common although your doctor might disagree. It is associated particularly with ingestion of sugar becaus that is what yeast uses in the process of fermentation. Sometimes the fermentation is so active that you can hear "bubbles and squeaks" from your belly. This is known as "brewer's yeast syndrome. You need bowel and body treatment of the infection.