I have never heard this 3 weeks on/3 weeks off, but everyone has their own philosophy of what works.
How long are you running the sustenon for mon cheri? in total?
and yes you can take t he dbol again now.
normally you would run your cycle, 6,8,10,12 weeks doing your pct and then you would stay off the AAS for as long as you were on or twice as long before doing next cycle, giving your body an opportunity to refresh and your natural self to be working properly once more