"However, over time, it seems to be less effective now. But, if I go off it, all hell breaks loose, so I'm quite stuck"

Do you do a full month cleanse? Perhaps you should try varying the cleanses you use, or use a cleanse with many herbs like humaworm. Do you take the cleanse herbs just before eating? The idea of this is not to feed the parasites anything without getting some of the parasite cleanse herbs with it. If you add raw garlic(best after the meal though to avoid stomach upset) and olive leaf extract when cleansing, they will be more effective.

Perhaps if you can identify the parasite then you could take prescription drugs against it. The prescription drugs are very strong, and sometimes it just takes one dose. Sometimes there is a strong die off reaction from them. I like using herbs first, but if the herbs don't work, then using a prescription drug seems like a good idea.

You could also try taking a large dosage of an herb with almost no toxicity like turmeric, ginger or olive leaf extract and see if that helps. A large dosage of raw garlic might be potents, however that would probably be too irritating on the stomach. It is best to limit raw garlic to a clove(section) or two at each meal, and eat it after the meal. Raw garlic on an empty stomach can be very irritating.