Hi Lousial - last month I had really a really crampy tummy and loose stools (not quiet diarrhoea) from about 2 days after my AF was late and and lasted another week or so. I did get a BFP but had a loss - I was only 5.5 weeks. My work mates & children I care for had had tummy upsets previous to this and I thought I had a bug at first. Am not sure if the loose stools & cramping was a preg sign, somthing to do with the loss or a bug. I was worried about how I was feeling at the time and posted here (1st tri i think) and asked for advice. Some ppl said they had had similar symptoms before BFP.
Hope ur tummy settles down and things go well for you.
Unfortunately I always get diarrhoea around the time of AF. I had heard that constipation is a common pregnancy since but I guess everyone is different and experiences different signs and symptoms - I hope its a good sign for you x