Hello and welcome to HCM.
Thank you for your query.
There is no chance of pregnancy
if you have had your last sexual contact before your period. All your symptoms could be related to another condition all together, in your case a gastrointestinal condition. Please consult your doctor if these symptoms persist.
I hope I have succeeded in providing the information you were looking for. Please feel free to write back to me for any further clarifications. I would gladly help you.