That is great news about your fermentation starting. The yeast look really active in your photo. Your lemons must have been much sweeter than mine.
It is not unusual for the pH to drop during fermentation. So if you’re near the limit of your yeast’s acid tolerance, you may stress them. As Johnd recommended, I would check the pH. If you don’t have a means to test the pH, try tasting it. Is it super tart? My lemon wines taste well balanced and ready for a splash of vodka before I pitch the yeast. I do adjust the pH with the aid of a meter prior to pitching the yeast.
Also, you might want to consider adding a little more yeast nutrients (DAP) and yeast energizer. I typically follow DangerDave’s Dragon Blood recommendations, which is to add 3 teaspoons of DAP and 1 teaspoon of energizer for a 6-gallon batch. I step-fed the yeast in my current batch. The yeast really seem to like that.