Everyone is different in terms of brain chemistry. If you are having success with it then good, I did not. It was awful for me, but it turns out I had genetic markers that showed signs of adverse side effects with it (and most other standard anti-depressants).
Just be careful, in particular, it is known to cause some very odd sexual side effects including priapism of the penis and/or clitoris, and triggering hypersexual mood swings and spontaneous orgasms (last one is very rare though).
Definitely, DO NOT take this drug outside of prescribed dosages. 100 mg is generally the max recommended dosage for this drug, and taking larger dosages can increase chances for heart arrhythmia (I had this a few times actually was very unnerving).
If it is working well for you depression and sleep problems then that is good though, just follow instructions.