于是我开始怀疑春天来了。

I began to suspect that spring is coming.

youdao

然而一年过去了，我仍旧没有取得突破，于是我开始怀疑自己。

After a year or so, however, I still hadn't received a break and began to doubt myself.

youdao

顺便说一句，出现了最近我的机器编译的代码中明显放缓，即使是旧的代码，以前跑得很快，于是我开始怀疑。

Incidentally, there's been a noticeable slowdown in compiled code on my machine very recently, even old code that previously ran quickly, hence I'm getting suspicious.

youdao