Hi Steve....welcome to the forum
Does the oil smell of diesel, e.g. is the fuel going past the rings and into the oil?
If so, then the oil will be diluted and require changing immediately as this can lead to ingestion within the combustion (runaway engine) which in the long run is far cheaper to replace the oil than the engine.
Alternatively, it sounds also like the fuel return is blocked, (fuel filter, return valve, etc)
Let us know what you find out