Hold on a moment. Rather than recommending taking antacids with Milk of Magnesia, as I stated in my previous post, it is not a good idea to be taking it at all. It is a laxative after all and you can become dependant on laxatives up to a point when you may not be able to open your bowels without it. Also, you should not be taking OTC antacids at all without a proper diagnosis and knowing why you are taking them in the first place and definitely not to counteract the effects of MOM, which it is not a good idea to take in the first place either.
Whatever happened to thinking about and taking a look at your diet, your fluid intake and your exercise levels. Altering these could stop you from being constipated in the first place. Add some more fiber/Metamucil to your diet and cut out junk food and soda and you could be half way to solving the problem. Add a little more water and exercise and these help too.
Just by altering a few things in your lifestyle, you would not be constipated in the first place and so would not need to take MOM in the first place.
If after all this you are still constipated, then I would suggest glycerinne suppositories rather than MOM.
A case of simple constipation should resolve with these measures and it is always better to treat the cause rather than the symptoms.
If constipation does not resolve, then you should see a doctor, as there could be more to it and it is always possible that you have something such as an intestinal obstruction, which of course needs urgent treatment.
However, most cases of constipation will resolve with simple measures without having to resort to laxatives. Try practicing a little preventative medicine and you could save yourself a lot of money rather than trying to cure what you have created yourself and with laxatives at that!!