Is there a common way to express the reason for something after stating what the something is? All the ways I can think of explaining situations involve putting it before. I.e. ～から～です. I was hoping to say something along the lines of "I had this thought because ~".
There are many ways to do that. I will only introduce the patterns most often used by us native speakers. Note that to do this in Japanese, it will basically take two separate sentences. In informal writing, however, one could get away with combining the two into one by replacing the period after the first sentence with a comma.
1) 「A sentence. なぜなら～～～からです。」
2）「A sentence. ～～～からです。」
3) 「A sentence. というのは～～～からです。」
4) 「A sentence. ～～～という理由からです。」
To express "I had this thought because ~~.", you could say: