Is it normal to always fall sick postpartum?

I gave birth 4 months ago and have been falling sick a number of times with sore throat, cold, fever. Usually recover in around 1 week’s time. 2 weeks later, fall sick again. Is this normal? I’m exclusively pumping and it makes me exhausted. Wonder if this is affecting my immunity? Been eating a balanced diet, doing some exercises. #firsttimemom #FTM