So about a week and a half ago, I decided to try my hand at making a starter, and soon, sourdough bread! I started the starter with 1 cup of wholewheat flour and 1 cup of drinking water. I also added a teaspoon of yeast and a teaspoon of sugar to it. I fed the starter for about four days by discarding half and then feeding with half a cup of water and half a cup of wholewheat flour and after the initial fermentation, stuck it in the fridge. Now, I've noticed that the texture of the starter is quite runny. During the feedings I have slowly been cut down on the amount of water used. As of this Monday, I used about 125mL of flour and 100mL of water, and the starter is still quite runny. Am I doing something wrong?

Edit: I forgot to mention that I leave the starter on the counter overnight after feeding it before sticking the starter back in the fridge.