napping troubles

Gillian • After 18 months of trying my husband and I finally got our big fat positive!!!!!!!
My son is 6 months old and will only nap his long nap if he's being held!!! He sleeps through the night just fine on his own.. if I don't hold him for his afternoon nap he will only sleep 30-40 minutes instead of 2.5 hours if held.. any tips to get him sleeping on his own would be great..