Cold again and again. Again and again!

My 3 year old weight around 13kg getting cold again and again from last 2 months like after 10-15 days her nose start running or sometimes it's congested for many days is it normal in December she was getting high fever along with cough cold fever stay for 3 days but cough and cold last for 10-12 days after 15 days again she's cold and cough start (mild) and stay for 7-8 days and then again after 10 days her nose start running with sneezing....mostly her cold is like congestion she force to clear her phlegm from nose ... if we go with Dctr they always prescribed antibiotic with other medication is it ok to giving that much antibiotic to toddler she is already taking antibiotic 3 times in 2 month what is the reason of cold again and again