Are you maybe overworking your muscles? It's possible that, given your muscles are weak and healing from all of your activities, that playing bass has overworked your tendons. Also, you may want to evaluate your movements in all of those other activities: they might be contributing to your condition in small yet collective ways. I know that bike riding at least can be hard on the tendons. My personal, nonexpert opinion is you reevaluate *all* of your activities: easing them all back and paying attention to movement. Take whole days off of all of those activities too.
My roommate is currently recovering from tendonitis he picked up from playing Salsa piano. It's been 5 months, but he's recovering. At some points it was so bad that he would get shooting pains from basic daily activities. The only thing that helped was dropping Piano *entirely, severely limiting physical activities with his hands/arms, adjusting his posture and movement, and practicing very limited lightweight arm exercises. Now he's experiencing no pain and has even started playing the piano again.
Overall it's been a very trying experience, requiring patience, restraint, and consistence.