I am a self-funded PhD in the US paying for my expenses with a combination of loans, my job as a tutor, and personal money just for tuition purposes. It is possible to do so but expect a lot of long days and longer nights and be ready to put in a lot more time and effort as a fully funded PhD student does. If you have enough strive and ambition to be able to attain your PhD than it shouldn't be much of a problem. Hopefully this helps!