stiffness in lower back and overweight

I am 37 years old and 110 to 12 kilos overweight,my height is 5.5 feet.
I have two children 3 and 8.
I exercise regularly.
I walking up a hill (10 min)
Walk and mild jogging for 1.5 hours.
I do this between 3 to 5 times a week
Non-vegetarian diet, but with a greater amount of fruit and vegetable and vegetarian diet.
I eat breakfast and dinner at a fixed time.
Lunchtime varies depending on work.
I feel stiff lying on my back.
Getting up in the morning is tough due to the stiffness in the lower back.
I do a lying half twist (dont know the proper asana name) before getting out of bed which also relieves my back considerably.
I also need to walk around the house for 15 to 20 minutes before my back is completely freed from stiffness.