Quite possible. However, at times it may be because of food reaction. I presume the doctor must have given you some antibiotics for the infection. In so far as rectum is concerned, if you are going for poo several times a day, the rectum and anal canal gets swollen. The cramps may also be the result of stomach infection due to food reaction. In case it does not improve in another two days then you must consult your GI, who may recommend a colonoscopy. Have patience I am sure that it may not be UC and just a reaction which will go away. Take care. Don't worry as the stress would delay your recovery.