Forecast Model recognize future trend
Before going into modelling, I guess you can do a bit more of exploratory analysis(month by month, year by year). If you find any trend or seasonality and so on.

Why did you go to RF directly without using basing Techniques like ARIMA, ARMA, Exponential Smoothening and AR so on.

Sometime RF might not give you as good results as Base models, I think you don't have trend, this is from your graph(but not certain). If you can try doing some research and see if there are some external factors which are effecting your demand. Why did that happen and what is the root case for it.

To your model to understand, it needs some feature which explains its spikes somehow, it can achieved by doing feature engg/ research