I'm also ex-runner - stopped mostly due to time, so started biking to work as it's faster than running.
If you have or are willing to get a heart rate monitor, your hr has excellent correlation to your actual effort level, taking the wind, softer tires, smoother road, and your own energy level out of it.
A good approach may be to use a hr monitor as a 'speed limit' for a while, and just try to maintain a hr of 120-150 for your duration. That SHOULD be slower than you are currently going if you're too sore for more than twice a week, and should allow you to bike more often. Key is keeping the intensity from getting too high, which should also allow you to bike for a longer time, as well as make it more enjoyable. Key to this is to keep doing this and not get hurt!
Even for your stated goals, after you've done that for a couple months there's value in a weekly harder effort, but in my opinion, a good point to start.
I'm assuming your healthcare professional has recommended you exercise more. If so, I assume they have also told you whether there are any adjustments about blood sugar monitoring, whether your personal condition means you should carry sugar, etc. If not, ask.