Some states don't require a specific "license" to work as a personal fitness trainer individually, but as those rules vary from state to state, you'll want to check with the Pennsylvania Secretary of State.
You may also want to establish a separate bank account for your personal training business, rather than run everything through your personal account. That's the bare minimum to set up, but you won't get any limited liability protection should an accident occur in your client's home and your insurance isn't sufficient to pay it. You may want to speak to a business attorney in your area to get a better sense of your options and the costs.
Related: Keep Your Business and Personal Finances Separate
Related: Business Structure Basics
Nina L. Kaufman, Esq. is an award-winning New York City attorney, edutainer and author. Under her Ask The Business Lawyer brand, she reaches thousands of entrepreneurs and small business owners with her legal services, professional speaking, information products, and LexAppeal weekly ezine. She also writes the Making It Legal blog.