2, see if it is: vitamin D, calcium, and other elements are lacking, or something else.
3, still so small, you can compare with the babies around you. If you find anything unusual, go to the hospital.
4, so as not to lose the best treatment period.
5. If there is a lack of elements, add them. If it is other related diseases, it must be checked and treated.
It's hard to get good answers online.