Please do not take Milk of Magnesia. This may have caused a lot of your problems. Your body can become reliant on this to have bowel movements and it can also alter the composition of your stomach acid making it too alkaline, thus causing you more problems.
If you are getting constipated, then take some Magnesium supplements to help with the constipation. This is a much more natural way of relieving it. If this does not work, then try drinking some baking soda, this can also help.
I would say that when you take Acidophilus your weight stablilises because your gut bacteria become rebalanced and when your system is balanced in this way you should neither gain or lose weight.
Hope this helps and please don't take any more Milk of Magnesia. It will only make your problems worse in the long run.