Toddler constantly has a cold

My almost 2 year old is constantly sick with a cold, runny nose, cough. This has been happening for the past 2 months. She will go 2-3 days and then it will happen again. Idk what’s causing this….the only thing I can think of is the fact that she didn’t even have a cold until after she was 1 because I was a crazy germaphobe so maybe her immune system is just starting to build? I take her to the doctor and she does all the test and then tells me it’s just a cold but idk how she’s getting so many colds….