While I don't have any personal experience with Miralax, many of our community members do. For example, Kim has shared her experience here: https://irritablebowelsyndrome.net/living/talk-constipation, alongside many other options to treat constipation. Laura also describes having success with it for a while here: https://irritablebowelsyndrome.net/living/prunes-dates-constipation, before having to resort to other coping strategies. However, I couldn't find any information about it being too strong, so I'm wondering if you're just not tolerating it very well?
If you haven't already, maybe you could try managing your IBS through diet, like these foods that can help with constipation: https://irritablebowelsyndrome.net/food/constipation-food-tips, or even supplements, as described here: https://irritablebowelsyndrome.net/living/vitamins-constipation —unless of course you've tried that all before.
Hopefully, other community members will chime in soon.
Hugs, Karina (team member)