Hello,
Welcome to the ehealthforum and I am really glad to help you out.
If you are having your periods, then chances of pregnancy are nil.
Most likely it looks like gastroenteritis to me. Gastroenteritis is an irritation and infection of the digestive tract. Take adequate fluids throughout the day. The BRAT diet (i.e. bananas, rice, applesauce, toast) or soft easily digestible semisolid diet can also be taken. Antimicrobial therapy is indicated for some bacterial gastroenteritis infections. However, many are self-limited and do not require therapy. The specific antibiotics are taken for specific bacteria after stool culture. For that you need to consult a physician.
I sincerely hope that helps. Take care.