Quick question

My three month old baby girl has been having diarrhea for past one week now.... but she is having one poop a day. No fever... she is drinking fine... the only thing I have noticed lately she has been whining in her sleep a lot... I called the doctors Offic and their front desk young lady mentioned if they baby poops more than three time a diarrhea a day then bring her in...could it be UTI... if yes how do you treat it in three month old baby girl... thanks in advance ... sorry about the bad pic