You sound like you could have a significant tolerance to DXM already. DXM is moderately addictive and can produce physical dependence similarly to regular ketamine use.
You mentioned in another response that you can't find products with only DXM. Depending on the other active ingredients, this can be incredibly dangerous and harmful over time; especially at doses as high as yours. If APAP/paracetamol is involved you're regularly way exceeding the dose that produces liver toxicity. Things like ibuprofen are similarly harmful at high doses.
Even DXM itself is presumably neurotoxic to some extent. A lot of sources suggest leaving two weeks or so between uses to avoid tolerance, dependence, and potential toxicity.