Internal steroids can produce acne, but it doesn't seem likely that there would be enough absorption from Kenalog in the skin to do that. On the other had, I don't know what your doctor means by saying that these injections would help acne, especially severe acne.
"Huge amounts of hair loss" and severe postadolescent acne need to be addressed and treated in their own right. I would ask your doctor about that, and consider getting another opinion as well.
Dr. Rockoff