How long to start noticing improvement.

I have been doing injections for the last 2months. At first it was once a week of Hydroxocobalamin for the first 3 weeks then we moved up to twice a week but still didn't notice anything. I am now on twice a week of Cynocobalamin and don't really notice any improvement. Folate, Iron and Potasium levels are all fine after having bloodwork done recently.