Hi,
Now that you have posted about it,i remember we had a little bit of similar problem with my son,and i remember our doctor checked his blood calcium levels and did an x-ray,his calcium was low and his x-ray showed mild rickets,he was then put on calcium supplements,what i wonder now is that i didn't know how much Vitamin D is important at that time,but Vitamin D deficiency can also be a cause of rickets or bone softening,especially the kids who are exclusively breast fed are mostly deficient in Vitamin D,one more thing i remember that doctor asked us to let him play in morning sunlight,and that was obviously for vitamin D.He recovered fine.
Alhumdulillah.
So lets see what your doctor has to say,checking calcium and Vitamin D levels would be a good idea.
Good luck and keep updating.
Zaini.