I take Vit B12 injections - I do it myself. You can get a 6 month vial of B12 for about $5 so don't worry about the cost.
It is true that in certain circumstances Vit B12 supplements do not work when they are taken by mouth because often someone with a B12 deficiency has the deficiency because they cannot absorb the vitamin.
However, if the vit B12 is injected directly into your blood stream it will work ( you by pass the need to absorb the vitamin through your small intestines)
If you are B12 deficient due to being a vegetarian then you may benefit from an oral Vitamin - However, if you are deficient due to an absorption problem or pernicious anemia then you need the injections.
The injections do not hurt and I suggest for convenience you learn to do them yourself.
And, YES, YES, YES it helps with the fatigue -
Vit B12 helps with the formation of the red blood cell - the red blood cell is responsible for carrying oxygen throughout your body if you are deficient you will feel fatigue and run down due to the lack of oxygen carrying red blood cells in your body. This is a type of anemia, another type of anemia is iron deficiency anemia.
PS: you won't notice a difference the day you receive the injection, give it about a week to notice increase in energy
I just want to add regarding people who say that it doesn't help, the reason it doesn't help is because they are not B12 deficient. It is not a miracle energy solution - It works for people who feel fatigue and sluggish from having B12 deficiency anemia. It helps replace a vital nutrient in those that are lacking it, just like when people with iron deficiency anemia need to take iron suplements - same thing different supplement. Taking iron when you don't need it is not going to magically give you more energy!