Voltage form at diode bridge
It looks like your differential equation is not set up correctly. The basic equation to start with is

\$ I = C \dfrac{\mathrm{d}v}{\mathrm{d}t}\$

and for the resistors

\$ I = \dfrac{v}{R}\$

That means you should have something like 

\$ \dfrac{\mathrm{d}v}{\mathrm{d}t} = \dfrac{-v}{R_1 C} + \dfrac{V_s(t) - v}{R_2 C}\$

where I've buried the rectified sinusoid into the \$V_s(t)\$. 

Notice that C appears in the denominators, not the numerators.

Also, the source only charges the capacitor through the 90 kOhm resistor, so with your current values the charge up has a time constant of 90 s. You'll want to run the simulation for 5 or 10x that time constant to see the output settle down around the steady-state value.