我又仔细考虑了一下。英语如何说呢

I had a second thought over sth.

second thought的定义：thinking again about a choice previously made （是指重新认真考虑以前所做的决定，类似于中文“三思”）
同义词：reconsideration, afterthought, rethink

其他表达也对，只是从语言习惯上而言，second thought比较受老外青睐！

I think it over again.

I think it over again.

我发了后才发现和1楼的答案一样，啊门，你速度太快了

I have carefully considered what

I turned it over in my mind for another time.
I think twice of it.