I am a Grade 9 student. I have a problem, and I do not know how to deal with it. I have a lot of homework every day, and I have no chice but to do it. I often have to stay up late. Then I sometimes find it hard to stay awake the next day.

这是初中九年级上册的课文。请教老师：这里的the next day - the 是否是否正确？这里next day 或 the next day 都可以吗？

语法书上说next day 或the next day 只能用于过去或将来，而不能用于现在。可是为什么Then I sometimes find it hard to stay awake the next day呢？

请教专家详解。谢谢！