OK thank u.. We haven't introduced outside milk yet.. But he is given Similac advance from his birth since he was preterm.. Doctor had given few drops but still no improvement

As the baby is taking solids there is a possibility that there is some food item which is not suiting him. The most common item can be milk. If you have introduced outside milk like cows or Buffalo milk please discontinue and see if that makes a difference. Discuss your concerns with the pediatrician as well.