Am I experiencing side effects from hydrocortisone cream?

All corticosteroids are basically a form of hormone and in time will thin the skin which is why the instructions always advise apply sparingly. I doubt if the hydrocortisone would cause breast enlargement though and I think that is most probably genetic and suggest you would have grown cup sizes anyway. If your mum and nan are on the larger size then your mitochondrial DNA would predispose you to be larger too.