i hope someone who actually knows can chime in here. as far as i know, if you have hod one round of Antibiotics , you may have dysbiosis until it is corrected. i here what you are saying about symptoms and the relief of them. there is more to this, however. i quit supplementing b12 a long time ago.
what i did was put the b12 on my skin and then rubbed dmso on top and let that carry the b12 into my tissues. it worked, i felt it, but i dont know how good it was for me. lol