Sewage infrastructure

I live on a small downtown street in a new condo. About 6-12 months ago I noticed our toilet wasn't flushing as vigourously. And its gotten progressively worse since a another condo across the street starting taking occupancy. Our plumber said it was a 'load issue'. Is this actually possible - that a bunch of new condos on a corner could create such a problem, overwhelming the sewage system?
Perhaps coincidently road crews have just started tearing up the road to place new pipes.