Hi and welcome to the forum! I am glad that I can help you.
You want to know the cause of the symptoms that you experience.
Changes in the stool such as runny stools in degrees between water consistancy and normal stools, may appear due to diet if there is no other underlying medical condition. Increased intake of water and drinks, especially sweet ones (because they increase the osmolarity in the bowels and initiate bowel movements), may cause loose to watery stools. Increased consumption of fruit (such as peaches, strawberries, pears, apricots, etc.) and vegetables may increase the peristalsis and cause bowel movements.
Given the data that you described, you are experiencing changes in the consistancy of the stools. Eat regularly a low fat diet(avoiding pork meat or meat products such as salami, sausages, etc.) with an increased intake of dietary fiber which can be found in vegetables and fruit. Avoid skipping meals or drinking liquids rich in sugar to avoid diarrhea. See your doctor if you experience additional symptoms such as increased body temperature, exhaustion and vomiting, to rule out any intestinal infection.
Please keep in mind that I provide medical information only. I am not able to diagnose medical conditions online. Please contact your doctor for further advice and information about diagnosis and treatment of your current condition.