Hello, Getting late on your periods 2-3 days is pretty normal, and having a normal period suggest everything is fine and that you are not pregnant. You actually never required that pregnancy test after you had periods. This is also unrelated to your diarrhea. There are multiple causes of diarrhea, the most common is gastroenteritis. It usually results after you eat or drink contaminated food. The usual treatment depends on the severity of symptoms. You should try to take lots of fluids and Oral Rehydration Salt (ORS) available OTC. Alongwith that, try to eat fiber rich food, bread, rice, tea and yogurt. If the symptoms don t improve in a day, your physician might prescribe you metronidazole 400mg thrice daily for 5 days. Thank you.