I could make some suggestions in terms of diet. If you suspect parasites and you have chronic constipation, you should quit sugars and refined carbs completely. For me, i have always thought i eat really well (only organic) but after i got sick i realized i ate the wrong combinations and in the wrong proportions. Your diet should be 90 % vegetables (steamed or stir fried), and the rest a bit of complex carbs and proteins. Not sure how is your digestion, or stomach acid? When i was very sick my stool was full of undigested food. I then stopped with all raw food. Everything i ate was well cooked and warm, even for breakfast. I use lots of herbs and spices that help digestion, like cinnamon, peppermint, coriander, black pepper, fennel, cumin, turmeric, cloves, garlic, red onions etc. I did do medicinal herbs, some successful some not at all. Now my digestion is much better, no undigested pieces and stool really regular. I think if you eat lots of vegetables and keep the balance with complex carbs and the protein, you should have enough fiber intake. I also drink only warm drinks throughout the day, such as herbal teas pr just warm water. I think this is a good start. Of course if you are vegan then you use vegetable proteins but make sure you eat 9 cups of veggies per day. Your constipation and parasite problem is not cured solely with this diet but it will help. parasites can cause constipation, but also other organisms that can overgrow in the intestines. Make sure you rule out all possibilities (yeast, bacteria overgrowth) before moving on to the parasite cleanses. In my opinion commercial dewormers are really not effective, and none of the popular herbs (personal experience). If you have a chronic condition you will need to cleanse and diet for months if not years before you see results.
This is a parasite forum but i do want to mention that constipation and parasites are manifestations of mental inbalances, stress. Detoxing the mind is a powerful way of improving your health. For me meditiation made a huge difference.
Ps. And despite the misbelief nowadays milk is really good for you digestion. I use it to make porridge in the morning (i buy local organic milk from a farm).
I wish you a better health!