After you start refeeding, eat raw foods for equal number of days to your fasting days ( I just can't say this correctly, ever). Then do a stomach acid test. You can can google the protocol or YouTube it. If you fail the test then do the test again after a few days. If you fail then you should take betaine HCL tablets half way during your major meals and take all B vitamins. That article has good details that you should follow.
ACV is also very helpful. Gut microbium will get healthier with probiotics.
I have a few questions for you, how did you take B12 shot? Self administered or through a doctor? How often do you take these shots?