Could be several things. The key is don't give up, forget everything about guitar (except where the notes are...lol), think in terms of a rhythm supporting instrument. Set the amp EQ flat to start. Same on the bass if you have active electronics. If not, open the volume, adjust the tone to taste. Can't remember what bass you have.
Keep the amp tone clean. No clipping. If you want any dirt, use an overdrive pedal with a bass control on it. However, I've seen guys use a bone stock TS9 in their bass rig to tighten up the bottom and give it a little kick. But that is after getting the fundamentals down with a simple clean sound.
With a good setup on the bass, it will be enjoyable. If you do good setups on your guitars, do it on the bass. Their's loads of videos on YouTube on how to do it. And the same principles apply, just with a longer scale.
My bass amp is an Ampeg Portaflex 500 head and GK 4x10 cab. I love that setup. The bass player I'm playing with now has a Markbass 2x10 combo and while he had it being worked on, picked up a Fender Rumble 100. That amp crushes!! He doesn't do too much with the EQ and he plays a Fender Jazz bass. Fills in perfectly.
Listen to Badlands. Greg Chaisson lays down some great bass lines with a solid tone that fills in great. For simple stuff, can't go wrong with playing along with AC/DC to lock in with the rhythm. What you gotta do is lock in with the drummer. There are times where playing what the guitarist does is necessary if there's one guitar but any other time, lock in with that drummer, especially the bass drum.
But, again, flat EQ, good setup, keep it simple. Progress from there.