How do I test the hypothesis that x (numerical) increases with y (numerical) and z incidence (categorical) over time, in the same time that both y and z are also affected by the increase in x? In summary, X is fueled by y and z, but both of them are boosted by increase in X over time.

I cannot say that y and z are independent, right? Do I need to perform 3 different models? 1) x as dependent, 2) y as dependent, 3) z as dependent?

What would be the best model to test this kind of hypothesis?

Thanks!