First day of school is coming and I've barely done the massive amount of summer homework due to working on college and personal things. How can I stay focused and motivated?

Sometimes it helps to figure out the worst-case scenario that could occur so you know exactly what you're trying to avoid and when it would take place. From there, you can work backwards. What do you need to have done by what day in order to avoid doom? Maybe you'll need to hand in a certain paper on the first day of school, so you'll need to write it by the day before, so you'll need to do the research by two days before that... You might stay motivated by keeping the worst-case outcome vividly in mind. Not the most cheerful way to get things done, but it works in a pinch.