Had b12 injection a week ago and it relieved some neurological symptoms. been taking sublingual b12 since but symptoms coming back? what could it be

Takes time: Depending on how long your vitamin B12 deficiency has lasted and the amount of damage done, time to symptomatic relief after supplementation varies. In other words, it can take months (or in severe cases, years) for symptoms to abate while on vitamin B12 supplementation. Be patient and see your physician for further questions. http://www.nlm.nih.gov/medlineplus/ency/article/003705.htm

Too early or?: Possible issues to consider are 1. it is too early to tell, keep treating 2. you are not absorbing the sublingual b12 3. b12 deficiency is not the cause of the symptoms Depending on how long you have used the therapy, you may want to wait a little longer or repeat the b12 test to see if the level has come up.