My Girlfriend Had Period On 23rd October And Then Again

My girlfriend had period on 23rd october and then again it came on 3rd of november and then again on 13th of november and after that the periods came on 11th of december. please tell me whether this is an effect of ipill or something else? Could this thing happen if Ipill would be taken on last week of october or first weak of november?plz tell me the reason