Unfortunately, many OTC pesticides do only last for a short time. They'll "knock down" the initial population but wear down in strength when the new eggs hatch.
Here in Georgia, flying roaches (lovingly known as Palmetto bugs which, I suppose, are supposed to make them sound less gross) are pretty common once the weather warms up. They're really pretty much impossible to get rid of totally because our winters never get cold enough to get rid of the stinkers.
Max Force Gel (which is safer than many of the sprays available) tends to work well as the roach will eat this stuff, go back to the nest, die and be eaten by all the other roaches who will then be poisoned. You might want to look at purchasing that.
Gail