It is good to see your concern for your colleagues.
Under the circumstances it would be appropriate for you to have an open talk with them. Tell them about your concern, let them know that it is not alright for you to end up doing most of the work as it stressing you out. It is quite possible that they may not realise the extra load they may be putting on you, as you have suggested you enjoy doing all the work that is given to you. Explain to them that you do not get any time for the things you would like to do, as the extra work is eating into your personal time.
Also, tell them that you wouldn't mind helping them out once you are done with your work, and still have the energy and drive to do some more. Hopefully, they will understand. You just need to be firm with them.
Remember, it is not WHAT you say, but HOW you say it.
All the best!