Thanks for your question.
The incidence of muscle pains with statins as a whole has been found to be ranging from 1.5 % to 5.0% in different studies.
This incidence is dose related as well , meaning that higher doses cause higher chances of developing muscle pains with this drug.
That means the chances of developing pains with this drug is around 1 in 20 at higher end of incidence and around 1 in 66 at lower end of incidence estimates.
Considering that 20 mg of atorvastatin is a lower dose the risk for you should be towards lower end.
Regarding depression the evidence is towards statins protecting against depression in people above 40.
Please read the study linked here.