confused about the character 就
有時我唔開心會喊，之後我就心情好啲。

You think there is something wrong with this sentence because 我嘅心情 (my mood) is a noun; 好啲 (better) is an adjective. A verb is seemingly missing in this sentence
It would be easier to rewrite the sentence as '有時我唔開心會喊，之後我嘅心情就會好啲。' (Sometimes I cry when I am unhappy. Afterward, my mood would become better) or '有時我唔開心會喊，之後我就會開心番' (Sometimes I cry when I am unhappy. Afterward, I would become happy again)
However, if you must use 之後我就, you have to treat 心情好啲 as a verb phrase
Example:
'有時我唔開心會喊，之後我就(會變得)心情好啲。' --&gt; Sometimes I cry when I am unhappy. Afterward, I (would become) in a better mood