It could be that you are allergic to one or other of the "excipients" (or ingredients) of the hydroxocobalamin injections you are having

According to British Society for Haematology (BSH) guidelines and NICE Clinical Knowledge Summaries (CKS), the primary beneficiaries include: Key patient groups who may require B12 injections include: Pernicious anaemia patients requiring lifelong hydroxocobalamin 1mg intramuscularly every 23 months following initial loading doses Patients with gastrointestinal disorders including those who have undergone gastrectomy or ileal resection, and patients with conditions affecting B12 absorption such as Crohn's disease or coeliac disease Strict vegans and vegetarians though oral supplementation is usually sufficient unless malabsorption is present Elderly patients who may have reduced gastric acid production affecting B12 absorption Patients taking certain medications including metformin (MHRA advises monitoring B12 levels in long-term users, particularly those with risk factors or symptoms), proton pump inhibitors, and H2-receptor antagonists long-term [6] Individuals with neurological symptoms such as paraesthesia, ataxia, or cognitive impairment related to B12 deficiency Pregnant women with confirmed deficiency (hydroxocobalamin for malabsorption

B12 supplements come in a variety of forms, including capsules, tablets, soft gels, gummies, and drops or sprays
Numbness and tingling in hands and feet Poor balance Poor memory and dementia Mouth or tongue soreness Depression Deficiency is primarily due to issues of malabsorption, poor dietary intake and pernicious anemia
It is sometimes used in conjunction with other metabolic support peptides such as MOTS-c or CJC-1295/Ipamorelin for comprehensive metabolic optimization