Hello,
Welcome to ehealthforum and thanks for writing
The possibility of pregnancy seems to be almost nil.First of all you had used protection during the act and if it did not break then conception is not possible.Secondly you also had intercourse after the periods which is considerably safe time.
Diarrhoea might be due to other gastric issues.Relax and wait for the next period.It is better to use protection during sexual contact for protection from pregnancy and various diseases.
Take care!