Do you candle your eggs? If you don't it is very easy to learn, candle them at 8 and 16 days, if a large number are not fertile or are aborting early you will know it.
There could also be a problem with the incubator. If possible put a second thermometer and hydrometer inside to double check temps and humidity. A lot of cheap digital thermometers also record highest and lowest temps which would be good since you catch watch it every minute.
If there is a problem with the incubator it can be worse than just a low hatch rate, it can produce crippled chicks.