Maret

Follow the product instructions and a proper schedule rather than my guess, because adding nutrients late in fermentation is not always recommended. Ten days and still actively bubbling is the better end of late. Do the stirring regardless, that part has no downside.

Hydrogen sulphide from stressed yeast, and you have named both causes yourself. No nutrients is the common one: honey is famously poor in the nitrogen yeast needs, and when it runs short this is what it produces.

The lemon juice is the second. Honey is already acidic and adding acid before fermentation pushes the pH lower, which is another stressor. Most recipes that call for acid mean afterwards, for balance, not at the start.