At what point does weight gain become something you should actually bring up with a doctor rather than just diet and exercise?

There's no single universal cutoff, but a few signs are generally worth flagging: weight gain that feels disconnected from any change in habits, weight gain alongside other symptoms (fatigue, mood changes, sleep issues, irregular periods), or when diet and exercise changes genuinely aren't budging things despite consistent effort over a reasonable period. It's also reasonable to bring it up simply because you want a professional opinion. You don't need to hit a severity threshold to ask. References: https://obesitycanada.ca/healthcare-professionals/adult-clinical-practice-guideline/