You just happen to be one of a large percentage of the population that happens to be a photic sneezer. If the research is correct, you are likely to be caucasian (and we already know that you are a female), and caucasian females are the most likely to report symptoms of sneezing when they go from darkness into light. Ask your father or mother if anyone if their family has similar symptoms, and you might be surprised to find your not alone. About 1 in 3 people have a similar response according to one study, although the actual amount of sneezing that occurs can be variable.
The response is thought to originate from the way that your nerves are wired, meaning that sunlight for some reason overstimulates the same nerve that is involved in generating a cough. As far as treatments go, there is not much that can be done other than to shade the eyes. One report seems to indicate that over the counter anti-histamines might reduce the symptoms, but that might be a bit much for such a simple problem, unless it is affecting you. If you have other symptoms or concerns, please speak with an ophthalmologist
, who might be able to offer further recommendations and would be able to review your medical history and do a complete examination to make sure there is nothing more occurring.