Hello Jack:
It is good to hear about your recent situation.You says that you cannot get used to the life in US and don't have any friends there.Therefore,I would like to give you some advice.
First and formost,you need to learn their life habits and show your respect to the local costoms.Second,good communication with your american classmates can help you integrate into them better.Third,you can participate in more outdoor activities,so that you can make more friends.Last but not least,do pay attention to your manners when communicate to others.
Those are my advice,I believe you could do much better!
Love
Li Hua
手打不容易啊，回复慢了点，楼主没说字数要求，按照汉语大概写了这么多，可能有些小错误，望见谅！