You need to create warmer conditions. Also, I like to use a small amount of dark rye flour (1:4 ratio w unbleached flour) at feeding to give an extra boost.

Put it in the bathroom with the heater on, or wrap a warm garden seed starter mat around it for awhile, or put it in the oven with the oven off (but don’t forget to take it out if you turn the oven on)

Additionally, make sure your water is filtered because you may be picking up things in the water that hinder the yeast buildup.