I literally feel your pain - I've had it for approx 18 months now.
2 visits to the physio and trying different exercises .... I've kinda resigned myself to accepting it now. It doesn't seem to be as bad as it was .... some days are worse than others, but the pain is usually manageable.
One of the stretches that I found helps is standing with your foot flat on the floor near to a vertical surface such as a wall (I actually do mine at the bottom of the stairs using the vertical part of the bottom stair). Bend your toes upwards and push your foot up against the vertical part of the stair and lean forward a bit. You're basically trying to get your toes flat with the vertical part of the stair so you're bending your toes at 90 degrees to the bottom of your foot - this will stretch you plantar fascia.
I usually do 15 seconds of that stretch, followed by 25 reps of stepping up and down a stair, followed by another 15 second stretch, then 25 more reps, followed by a final 15 second stretch.