Try jogging where there are lamposts, in the first week jog for the distance of four lamposts (or more if this is too easy) and walk for the distance of two, repeat this until you've been out for 30 minutes (or whatever feels comfortable).
Have a rest day.
Repeat this process throughout the week- one day jogging one rest day- if you can only go certain days have two rest days in a row if necessary.
On the second week jog for five lamposts and walk for two. Have the rest days still.
Continue this, adding one lampost to the jogging part each time until you feel comfortable jogging for 5k.