One shouldn't rely on the Epsom Salts to 'cure' your constipation. It's basically a laxative - which shouldn't be used often.
Address the constipation. Drink at least 2 litres of WARM water a day for 3 weeks and see if that doesn't make a difference. Take Udo's Choice 3X a day. Eat fruit. Exercise...jump up and down...rebound. There are many things you can do to get your bowels moving. Do a Bowel Cleanse (Holistic Horizons or Experience) Do a parasite cleanse.
1 tbsp of Epsom Salts in a cup of water should move your bowels within a few hours. BUT if you're severely constipated you may need another es drink a couple of hours later.