B12 normally takes a long time to drop - the body routinely stores a year’s worth or more. Folate deficiency is on a shorter time course, but it’s pretty rare for folks who eat leafy green vegetables and whole grains. Both deficiencies result in a similar type of anemia, with large red blood cells (*very* different from iron deficiency). Supplements themselves can make the tests unreliable, as can other things, so some care is needed to make sure the deficiencies are 1) real, and 2) not overtreated. If I were in your shoes I’d skip the next B12 injection and test again in more like 3-6 months instead of 4 weeks. I’d also be a little suspicious of the folate deficiency, since it can act just like a B12 deficiency in many ways.