I get B12 injections months, however, last week my GI checked my B12 level and it wasn't the greatest, but it wasn't in the low 200's. Mine was 313. He ordered an injection of B12 with a dosage of 2,000mcg, and said we'd repeat the labwork in three weeks. If no improvement or if it worsens.....my doc said he'd increase the dosage to 5,000mcg and we'd keep going from there.
I usually feel pretty decent after receiving the injections, but when it wears off....holy cow do I feel exhausted. I can tell when my B12 and Vitamin D are low. I become extremely moody, chills or cold spells, extremely fatigued, depression is worse, as is the amount of headaches I get, and I just feel horrible from head to toe.
Fyi...my GI also said that he's seen the dosage of these injections go up to 10,000mcg!!
I had asked him if I should take an oral B12 supplement to help out but he said it'd be a waste of time and money, as I'd have to take mega, mega doses of the pills to even attempt to make a dent in my numbers.
How's your son's Vitamin D level? I can honestly tell you that when both my B12 and Vitamin D levels are in the appropriate range and I'm taking them as required...I feel great! It's unreal how much of your physical and emotional well-being are affected by these vitamins when they're grossly deficient.
I hope your son's B12 comes up quickly and remains normal. Good luck with everything!