You don't look well.you'd better see the doctor.I [ ] .But the doctor said there was nothingserious.

You don't look well.you'd better see the doctor.I [ ] .But the doctor said there was nothingserious.
You don't look well.you'd better see the doctor.I [ ] .But the doctor said there was nothing
serious.

You don't look well.you'd better see the doctor.I [ ] .But the doctor said there was nothingserious.
did
你看起来起得不好,最好去看看医生.
我去过了,但医生说没事.

翻译：你（的气色）看起来不好，你最好应该去看医生！
选 。 I(had ).
But the doctor said there was nothing
I(had )—— 我早就有了

你看起来不太好（指身体）。你最好去看医生
我......但是医生说没什么大碍

did

did
你看起来身体不太舒服，最好去看医生。我照做了，但是医生说没什么大碍 。
这里I did 就是I went to see the doctor 的意思，用I did 表示更简洁，也避免了重复。因为后面有said所以前面用do的过去式 did.
希望能帮到你