Congrats on your son's successful surgery! I echo the other ladies' acknowledgment of your determination and commitment. I think you should give it your very best effort (which you are doing), and be sure to be compassionate with yourself if your nursing relationship has to end before you had planned. I had a similar problem with my second child, but for different reasons. I had one of the worst cases of thrush imaginable, which we were slow to diagnose and that was VERY resistant to treatment. When my daughter was 3 months old, it started becoming painful to nurse, and by the time we figured out what the problem was, I was bleeding and opening wounds every time I tried. I could only tolerate pumping 3 times per day on the very lowest setting, which I did to try to maintain my milk supply. I, too, watched my milk supply diminish slowly, and tried supplements, etc. I feel your pain about pumping and coming away with maybe an ounce. Anyway, I developed a profound gratitude for formula, since it enabled me to take care of my baby. (I never used formula with my first baby, nor have I had to with my third, but I definitely know now that sometimes it is really important). By the time the thrush was resolved and I was able to nurse regularly, my daughter was 6 months old. I was very glad that I kept pumping, even with poor results, since I believe that it was what allowed my body to keep producing milk at all, and that when my baby was allowed to nurse again, my milk supply came back somewhat. I never got back to nursing without formula supplementing, but I believe it is more because my daughter no longer was interested in nursing. I feel that if she had wanted to nurse lots, my body would have responded to that need. She ultimately refused to nurse at all at 11 months old. She is now 2 and absolutely thriving.
Sorry for the super-long response, but I hope it helps. I know how frustrating this is for you, and you are inspiring in your commitment. Perhaps try the suggestions that other women have made, and no matter what your ultimate result is, know that you have done above and beyond the call of duty for your lucky baby.