Shedding does not happen on a regular basis where you can say "gee it has been 4 weeks and no shed there must be a problem". It all depends on each snake and the rate of growth they are experiencing at that time. When they are younger they grow faster and tend to shed more often. As they age their growth rate slows some and the shedding frequency does as well. It is common that as full grown adults many snakes only shed once or twice a year.
I would not be worried, odds are your snakes growth pattern has slowed some and sheds will be less frequent now.