Try a bit more (like 500 mg) and take it all together right before bedtime. I find this timing helps with my morning bowel movement. (as well as sleep!)
Magnesium citrate has a better laxative effect than bisglycinate, so if you switch, you may be able to take less for the same effect.
You may also be low on potassium. Try 1/2 a banana or avocado every day.
Also make sure you are salting your food to taste. Do not limit salt.