Forecasting using GRNN (Generalized Regression Neural Network)

Hello Everybody,
Does Anyone know? I have a problem when using GRNN (Generalized Regression Neural Network). I use this neural network for forecasting of energy consumption. I have data about energy consumption from 1990-2015. The trend is going up. The most recent year is, the highest score is,. The pattern is 1 output and 3 input. when I predict for 2016, 2017, 2018, the value should always go up from before. But the all 3 latest year have same value of energy consumption with 2015. Can anyone solve this problem?