Persistent constipation after taking prescription antacids. Remained long after quitting. What's the cure?

Laxative foods/bev. Calcium carbonate is an ingredient in many antacids. Aluminum also does the same. Magnesium is more of a laxative and that is why many liquid laxatives mix aluminum and magnesium to balance the constipation/diarrhea effects of both. Stick to adding more fruits, veggies, juices, water to enhance softer bowel movements. If you do fiber-fill up with more fluids1.
Depends. What do you mean by constipation? Infrequent bm's or daily bm's that are hard and difficult to pass? As a start increase your fluid intake to 80-100 ounces per dya and avoid alcohol and caffeine sources. Take a mild laxative such as milk of magnesia (magnesium hydroxide).