what is causing/ how can i treat constipation?!

Lack of fibre, lack of fluids and lack of exercise can all cause constipation.
It can be a side-effect of medication, and a side-effect of many other illnesses (it can cause illnesses too, through autointoxication from the intestine).
But some people are just naturally prone to it unfortunately - it may be that the bowel muscles don't work as well as they should.

I'll give you a couple of options. My personal favorite is apple cider vinegar (ACV). Go to your local health food store and get the Bragg organic brand. Supermarket brands are junk. Mix 1 Tablespoon with some water (not hot) and honey or stevia. Drink this right before each meal. Do this daily and it will fix the problem. You will soon be pooping with ease! Not to mention all of the other benefits ACV has for total body health. Google it!

The other is a Chinese Herbal Constipation remedy. Very trusted brand. I use herbs from this company and they are wonderful. Good idea with the fiber. Try to never eat white bread or rice. For me, it has a way of pluggin' the plumbing.

EDIT: I just thought of this: You may want to add in a digestive enzyme as well. This helps so many people with constipation issues. The vinegar may be all you need, but if not, this would be a good idea for you. I like Now Super Enzymes (capsules). They really work great!

www.drshen.com/herbsforconstipation.htm
iherb.com (online store for vinegar)

Find something that keeps you loose and add it to your daily routine. Sometimes not eating enough can make you constipated.

Things you might try to stimulate your bowels are coffee, apple juice, prune juice, and even soda.

Drink it at the same time each day and you can help yourself be more regular.

Something different works for everyone... so think of what already works for you and just add it to your daily diet.

Hot baths can also help. Walking after meals too.

You might want to read: "Fit For Life" ~Harvey Diamond

Hydrate your system by drinking nothing but juice when you wake up (anytime between 4am and 12pm. Your body runs on an unchanging clock system.) Then continue hydrating your system with water-rich foods for lunch like fresh fruit and green leafy salads. Eat a balanced dinner. I will bet within a day, you'll start getting back to normal body functioning. Get those toxins out! Let the body do it's daily job (no pun intended). This doesn't have to be just a one time fix either. It's a routine way of life that helps your body do it's work. Oh, and cut way back on meat. Science seems to lead to the conclusion that humans are meant to be herbivores. Our bodies can break down plants a lot faster and more efficiently than meat.

www.drewjarrod.com/blog
http://www.fitforlifetime.com/

taking a magnesium supplement at nite will help you to go in the morning....I do not know your age, but if you are having sexual relations, having sex helps especially for men.

One litre of water is not enough, You should be drinking about three times that amount.