My Son Is Having Cold For Last 20 Days. It

My son is having cold for last 20 days. It cums n goes bk. He is two years old n goes to play school. Doctor said it is normal to catch cold frequently as he goes to playschool. He gets infected again and again from there. Doctor prescribed relent plus and nasal drops. For last one week he is not going to school nd m giving him regular medicines but still his cold not going. What shd I do?