You sound overwhelmed, and extremely frustrated. Chewing on non-food items is known as pica. Often pica can be caused by a vitamin or mineral deficiency: most often this is an iron deficiency. A simple blood test can rule this out. Chewing on walls with lead-based paint (usually found in older homes), can lead to lead toxicity. This can be quite dangerous. Hopefully, the "chewing on the walls" phase will disappear by the time your son is 2 or 3 years-old. Nevertheless, you should probably make an appointment with your pediatrician for further testing & advice.
I don't want to alarm you, but my 8 1/2 year old son has been dealing with Pica since he was about 15 months old. He has chewed on & ingested things like flowers, small pebbles, hair, crayons, pencils, erasers, bits of toys, clothing, dirt, lint, paper, etc. He honestly cannot stop. It has become quite a habit. Iron & mineral deficiencies, in his case, have been ruled out. His doctor thinks this behavior may be caused by anxiety. When my son feels the need to chew, we usually give him a pretzel rod instead. That way, his need for chewing has been met, and we have redirected this behavior so he learns to associate a need for chewing with food.
Maybe when your son starts chewing on the wall, you could offer him some type of food instead - possibly a teething biscuit, dry cereal, a cracker, or whatever you have available.
Good luck with your son. Please let us know what happens.