It is normal to get a little distortion in head shape of infants because of sleeping continuously in same position. But that problem usually resolves by itself by the age of 6 months when the baby starts sitting and becomes capable of changing position by himself. Your baby is 9 months old and using home techniques of giving massages and supervised tummy time and re-positioning techniques will be of little help now. You should consult the doctor soon for advising other treatment for your child as he may be suffering from Plagiocephaly.The skull of the baby is very soft and can be made to change the shape by applying external pressures. Cranial helmet therapy can be used to correct the deformation only by the age of 2 years as shape of the head is fully formed till then. If this is left untreated, the head shape can remain like this in future. Cranial remolding helmets and bands are advised usually. Ask your pediatrician.