Some great info on naturally treating constipation here
Some good info on constipation related disorders here
Something that I have used and really helps with gas, bloating and constipation is vegetable carbon products that usually contain more than just carbon. The one that I have used here in Italy is TrioCarbone and is really good.
Vegetable Carbon (aka Activated Charcoal) is not known to have any side effects. See here Also see here Products like CharcoCaps (see previous link) and Trio Carbone is what you need (usually over the counter).
Enzyme and probiotic type of treatments/products (e.g. Beano) have not helped me.
However after trying this new probiotic tratment I found it to be the most effective yet - in fact, together with cetrtain diet changes described elsewhere on this site, it has completely solved my problem.