first of all you have not mentioned that for how much period you have kept the cast ?
second, tibia fracture
usually takes 6 to 8 weeks to unite depending on the fracture, age and bone quality
as you had cast for your fracture for only five weeks you may need still atleast 2 weeks of cast support.
apart from that you should consult orthopedic surgeon for weight bearing advice.
you can also contact me with your reports on my profile.
wishing you best of health bye..