在英语中介词后面允许跟名词性从句构成介词短语吗?

不仅可以,而且很常用.构成介宾结构.如：
1.I am think about whether I should go.(这里whether I should go就是宾语从句,做介词about的宾语,组成介宾结构)
2.We should learn from what you have done wrongly.(我们应该从你做错的事中吸取教训)这句的宾语从句what you have done wrongly就是介词from的宾语
3.Whether we go depends on what you'll say.(我们去不去取决于你怎么说)这句的宾语从句what you'll say就是介词on的宾语.