Well, according to some researches, red eyes are caused by the enlarged and dilated blood vessels in the surface of the eye which has become irritated. Of course, you need to know that it could be a medical emergency or a non-emergency. In daily life, the most common causes of red eyes are irritants such as pet dander, blowing wind, dry air and sun exposure. And lacking of sleep can be the cause too. If contact lenses are worn for too long, they can experience red eyes too. So for your situation, it is very difficult to tell what the real cause is. And you can just go and see the eye doctor.