I usually plateau out at about 6 or 7 weeks.
You can:
increase diet,
end the cycle early, pct, and then go back on after a month or so
change/add meds
change direction - if you're not gaining muscle then try switching to more of a cutting regime and just try to shed fat instead
As said, up calories by at least 500/day - though when I do this i tend to gain fat, so Im tending to do shorter cycles now, as the first 6 weeks give reliably easier and leaner gains (for me - different people will react differently), so I just do 6 weeks or less, or if running longer aim to use the 2nd half of the cycle to tone up and
lean out rather than gain much more