Which one is correct please. Batman

吃完药之后，我的独自不疼了

吃完药（了）之后，我的肚子就不疼了。No need to add “又” here，“又”means again。But in this sentence, you want to say not painful anymore.

吃完药之后，我的肚子又不疼了。

不+adj，没+V
疼-adj，painful
不疼

the first one.but it could be better you could change “又” to "就" ， to imply a cause-effect relationship.

又在很多时候表示重复（Repeatedly）病好了，肚子不疼了，可是过了两天，我的肚子“又”开始疼了。

1) 不 should be used, "不 is often used to indicate an action in the future"
the difference between 不 and 没, https://www.cchatty.com/grammar/10342

2) not 又, 又 means "again", here should use 就, means "as soon as"

3) 了, here, can be omitted

so, the better would be,
吃完药（了）之后，我的肚子就不疼了。