I was in a similar place as OP, I stopped running a couple of years ago after some bad knee pain, put on loads of weight while still riding lots.
Then last september I said that was it I am going out running.
Started doing 3 miles three times a week 90% off road(hate running on pavements).
The pain soon came back, so started using ice packs on me knees afterwards.
I now run 4 times a week on average 8-9 miles per run but I have found a really good run of 12 miles that I do once a week that is 95% off road from my door that goes throug a dissused railway tunnel that is 600m long hardly see a soul while out too.
I have only ridden me bike twice since the new year as I am loving the running atm.(will be back on the bike after winter for sure.)
Oh I have lost 15lbs so far will be happy with another stone gone.
Get out there take it steady and it will come back to you.