I asked those questions to get you to think about the possible causes. I don’t know what the cause of the odor is, nor do I know what the odor smells like. But I do know that if the odor isn’t chemical (such as from your plastic plumbing), it is caused by bacteria. Bacteria create gas, the gas smells sulfurous, or like rotten eggs, sewage etc..
The chlorine you use monthly oxidizes the gas and kills some bacteria. Some types of bacteria will not be killed by your chlorination and trying causes them to produce a prtective slime. That can cause encrustations which further protects the bacteria. Chlorine is not good as a disenfectant with pH over about 7.2. Above that it is a good oxidizer. Chlorine raises pH, it is alkaline, or base. Your 2″ well, has little water in it and your pH will be sky high depending on how much bleach you are using.
Do you know what chlorine does to galvanized and all other ferrous metal? Are you aware of carcinogenic chlorine by-products? If not I strongly suggest you call in a water treatment dealer and follow his/her advise. In the mean tie, suspend your activities.
Quality Water Associates