What do you do at work? If your job involves a lot of standing,you may need better shoes or a shock-absorbing mat to stand on at work. Don't lock your knees!! Walk around at work if you can, and take every opportunity to move around, especially bending , kneeling or squatting to keep your knees mobile.

You can certainly walk 3 miles faster than 1.5 hours! Most people can walk ~3 miles an hour pretty comfortably - 4 mph is a "brisk" walking pace, or moderate if you have long legs Alternatively, you might try taking the bus partway and walking from the transfer point (or to the farther bus stop, whichever you prefer). Walking is much easier on the knees than cycling or running; just make sure you have shoes with good grips and good arch support, and walk at whatever pace and stride length is most comfortable to you. Speed walking is not a good idea

Grocery delivery is a great service, and a lot of shops offer it now, whether you go in to the store to pick everything out, or order online. Also consider using taxis for things like shopping trips.

Give your legs a rest for a few weeks, talk to a doctor, and then start up slow again. Consider alternating walking and cycling for your commute, and go slow building back up to doing all the errands by bike.

Also, something I've noticed is that my knees stiffen up really badly in the chillier fall weather. I'm investing in leg warmers...