I don't want to tell you what to do, but if it were me, I would up the temp. to about 101. I don't know what kind of bator you have, but I just kept the trough full. My humidity stayed around 40-45%. Then when I upped it on day 18, I placed a wet paper towel in the bator and the humidity went up to around 60-65% and everything turned out perfect.
You could see if your humidity level will remain if you start taking the sponges out one at a time, and if so, maybe you could put them back when it's time to up the humidity. If the humidity drops, then you know you will have to keep them in there.
Do you have any kind of air leak in your bator? If so, that may account for the humidity loss.
Sorry I couldn't be more help.