i have a degree in marketing, but i love trading stocks and I am very successful at it. Any advice on doing this for a career
If you are as good as you seem to indicate, then why do you need a career. Just trade for yourself and not have to answer to anyone.
However, if you get more fun investing other peoples money instead. You may consider becoming:
a investment manager for clients
a fund manager for a mutual fund
starting your own investment companies
or start your own investment fund (like a hedge fund)
Best wishes.