It sounds like plantar fasciitis. It is when the fascia gets inflamed and then will shorten in the night. That would explain the tightness and pain in the morning. Try doing some light stretches in the morning. Put your toes against the wall and your heel on the floor and then lean into it slowly. Don't force it! You want to gradually stretch the fascia back out. There are a number of different treatments. I did PT to stretch the fascia and hamstring, had insoles made for my shoe and have this very attractive boot

that I would sleep in while it was stretching. That keeps the fascia from tightening up overnight. I ended up with a cortisone injection that really made a difference.
I would check with your Dr. again. Labs would show an inflammation in the fascia, muscle or other orthopedic cause for your pain.
Best of luck,