Is my job asking too much from me?

Is my job asking too much from me?

I have been working for a non-profit for over a year now and I feel like I am getting more and more responsibility. In the beginning I was struggling with the workload, however, five months into it we hired a temporary assistant. It was a blessing from God! Everything runs smoothly and I am able to do more, meet all deadlines, and I run a much more efficient program. I have been getting compliments and thanks you's from our funders (especially one of the toughest to work with). I love it and I want to continue like this. However, once my assistant leaves, I am not sure I will receive anymore assistance and I feel that I will still be expected to perform the same number of tasks (which have increased because of my assistant) and have everything done in an extra timely manner. What can I do? I know that I will no longer struggle like in the beginning because I have become very skilled in what I do, but my assistant has been a great asset to the program and without the work she does (although mostly administrative) I will be once again swamped, stressed, and burnt out! Should I quit or am I just being negative and complaining too much? I am an hourly staff, not salary and I never get approved over-time. (I know it is not laziness since I give it my all 100% everyday and go above and beyond).