I have had my injections weekly now for nearly a year and have improved in so many ways, but by the time the week ends I am exhausted. I get my shot and seem to need a long good night sleep and a day or so to kick in. I go like gang busters all week with gardening, brisk daily walk, stretches, house work, entertaining, errans, and grandparenting a few days a month. I am wondering if B12 has anything to do with it, shouldn't my B12 levels be building up and storing? My deficiency is autoimmune.