Lump at the back of the Head.

Just few days ago I found out that was a little bump at the back to Noah’s head. It scared me till now. I brought him to GP and the GP told me it might due to his runny nose. Noah was prescribed with antibiotic. The doctor asked us to return to her if the lump still persist after a week.

Today is the third day, the lump is still there. I am worried.