My 5 year old son has the same problem, if he is biten close to his eye it will swell shut for a day or 2. Poor little guy. I have tried a few things too, if I spray him he still gets bit. After he is bit it does not take long for the bite to start the swelling, I watch him VERY close outside and avoid times of the day that are worse than others. Now this really works. After I see the bite I take a cotton ball and put rubbing alcohol on it, I hold it on there for a long time. I know this is the after the fact treatment, but I have not found anything as far as prevention. I have heard that a vitamin B complex works, liquid form tastes terrible but helps. I have an appointment with his Dr. and will bring this up to him. If ypu have found anything that works I would be pleased to know.