Scoliosis of unknown cause in such a young child is called infantile idiopathic scoliosis. It can go away on its own but must be watched carefully until it does.
In the past doctors thought this problem was caused by the way the child was positioned in utero. This theory has been disproven now.
In the 1950s there was some research comparing babies in England versus babies in the U.S. There was some thought that putting the babies on their backs was the problem. At that time American babies were routinely placed prone (face down) to sleep. The incidence of infantile scoliosis was much smaller in these babies.
A recent review of scoliosis in young children brought this point back up. Doctors suggest a need to look at this problem again. Further research on positioning infants and the possible link to scoliosis should be examined.
In the meantime, ask your pediatrician for his or her best advice. A baby monitor is a good idea while also checking often on your baby during naptime.