if he seems satisfied when you nurse i dont think i would be too worried. even if you are pumping a smaller amount, pumping is not a good indication of your supply amount, lo can always get more than a pump can. unless he is nursing more often or really fussy acting more hungry, i think you are ok. also, around 5/6 months nursing sessions become faster because lo becomes more effective and faster at nursing.
IF your supply dropped it probably IS because of dehydration from being sick, and you could try drinking a whole thing of pedialyte which is really good for rehydrating ANYONE. nursing more is the best way to up your supply, and pumping in between should help.
try not to stress!! its not good for you, baby, or your supply!!