Is it safe to drink alcohol after receiving a vitamin b12 injection and if so how much?

No. It is illegal for you to drink alcohol at your age. Alcohol is a poison that never did anybody any good, ever. So stay away from alcohol. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex, if you have sex. Get HPV vaccine.