I'm a bassist for our WT as well (and also nearly 45.
). I go through a DI and into the sound system with no external amp. The drummer and I share a Fender 1270P stage monitor - not without it's problems as he likes a different monitor mix than I do but, I think we've worked through it lately.
I can hear myself, though softly, and I can hear myself in the house as well.
Be patient, stick with it, find out what's going on as was suggested above and maybe try the headphones or buttkicker thing.