Might be worth looking into a new pickup, new strings, a compressor, cabinet type and orientation, overdrive and eq settings, where you stand relative to all sound sources in the room, any combination of the above, and a host of other potential gremlins.
Pickups have various output and voicing combinations. Some are better in a mix than others. Strings can have a significant relation and impact with the pickups.
EQ and overdrive can be helpful and troublesome. Overdrive creates compression, which can help, but sometimes a compressor is better for compression. The compressor could even out the level differences and push a more uniform signal to the amp. Sometimes cutting lows helps the mids and highs show up, as all things are relative and should be considered in proportion. A little overdrive will help things growl. So will picking closer to the bridge.
Different cabs have different dispersion characteristics. Bass frequencies radiate in all directions at once. Higher frequencies will beam from the sound source. If you stand right beside your cab, the lower frequencies will make it to your ears, but the higher ones will beam from the speaker in a more directional way, and you won't hear them as well. If your guitarists or other band mates are also playing frequencies in the range of your bass, you may run into phase cancellation issues, or the brain trying to process the sounds and determine the origin, which may trick you out of "hearing" them from your cab. You might also be getting into coupling issues with floors, walls, and/risers.
There are other gremlins possibly at work here, but these are some of the usual suspects.