conditional format to mark increase from previous column

Hello,

I've been learning to use excel through the aide of forums and I've stumbled across a problem and I just can't find the answer. I have a goal set for the year. With conditional formatting, each month will be set to either red or yellow based on where it stands in relation to the goal. I would also like to show an increase or decrease in productivity for each month. I tried to use conditional formatting with the formula: =IF(C2=D2, "", IF(C2<D2,"↗","↘")). The formula works on its own without the conditional formatting so I am not sure what I am doing wrong. I've attached a sample with all the conditional formatting and formulas in place.

Thanks in advance,
Ragbe