I was not good at my schoolwork, because I wasn't working hard on all subjects.

我的功课不好，因为我没有努力学习所有的科目。

youdao

When I was in junior high school, I was not good at sports because I was overweight.

我上初中的时候，我不擅长运动，因为我太胖了。

youdao

I was not good at expressing their feelings of people.

我是个不善于表达自己情感的人。

youdao

At that age (perhaps still) I was not good at biting my tongue.

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But I had to look at it from both sides: Of course, this was not good, not good at all.

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Since my vocabulary was not good at that time, I said, oh, it's ok.

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