Magnesium is the key. I had the same problem, chronic constipation for several years, because of parasites. I think they interfere with absorbtion of minerals, as well as blocking the bile ducts from the liver.
I would suggest trying a few things.
1. reduce your intake of refined carbs like crackers, potato, white bread, chips, etc as these have little fiber.
2. Eat only whole grain products when you do eat bread, etc. I eat "Sprouted" bread.
3. Try eating at least a handful of pecans and almonds in the morning and with dinner, if you have no nut allergys. Tree nuts have lots of minerals and magnesium and fiber. I eat some pecans, walnuts, or almonds every morning with breakfast.
4. Eat more veggies, if not already doing so.
5. If after all these, you are still constipated, try taking 100mg magnesium 2 times a day. Magnesium Citrate is what I take.
6. Take an Epson Salts bath 2-3 times a week. A study done in the UK showed that just taking a Magnesium bath raises your Magnesium level for 24 hours.
7. Cut back on Dairy products. If you look at nutritiondata.com, you'll see that lots of veggies have calcium, ( and nuts as well ). But veggies and nuts are balanced sources with magnesium as well. Calcium AND Magnesium together are used in the body and each one "Balances" the other. Dairy is NOT balanced, as it contains tons of Calcium without Magnesium. I each almost no dairy at this point. Nuts and veggies provide plenty of Calcium.
8. Cut any diuretics ( coffee, black tea, etc ) down in your diet. They cause water loss.
9. Drink more water if possible
Magnesium is critical to relax muscles and let bile flow and is used in over 30 enzymes in the body. We already eat way to much Calcium in the form of dairy in the US.
Try these things gradually. If you get diareria, your taking too much magnesium so back off.