Receive B12 shots mthly. Don't know cause of deficiency. Ok to supplement with sub-lingual B12 as well (5000 mcg)? I know it may be pointless.

Vegan? The most common cause of B12 deficiency is lack of B12 in vegan diet or mal-absorption. Are you anemic or were you just told that you have a B12 deficiency by the person giving you the shots? You may not need as much B12 as you are being told if you are not anemic. Check with your md again to make sure you are still truly deficient.