Sinus congestion after dairy consumption is not too unusual. I have experienced and read about dairy and its tendency to cause sinus congestion. For this reason I do not eat dairy on a regular basis. I can definitely feel a difference after a few days of eating yogurt, milk, or cottage cheese. My sinus are full and drain down be back of my throat. I have often thought this is also why my sister is constantly blowing her nose and coughing up mucus. She drinks more than her fair share (even organic) of milk.
Sinus Infections and Ice cream: I do not know about the various brands of ice creams and their contents. However, my body is lactose intolerant and whenever I give in to consuming ice cream [of the homemade variety,no less], in a few minutes,I feel the nasal clogging. Has anyone been tested for lactose intolerance? Sugar and other foods that do not agree with my system affect my sinuses adversely.