Well, if they were 18 weeks when you bought them, you should be getting eggs at any time. The stress of a new home could delay them, but if it's been seven weeks then they should be used to their new area by now.
Have you been getting a lot of rain? Is it very hot? Very cold? Extream weather can throw them off laying as well.
Perhaps it is the changing seasons. The less daylight means they will slow. Some year old chickens may only lay an egg or two a week. Very young hens may not start laying until the spring.
Hopefully, someone more experienced will chime in.