Weight gain!

Kate
This is frustrating,  I track and measure my weight very closely to make sure that I am gaining the right amount that my dr recommends,  I eat healthy and exercise 4-5x a week.  What I don't understand is that i seem I hover around a weight for a while and then all the sudden jump up 3 lbs and stay there.  It is so frustrating, anyone else have this.  I will be 16 weeks tomorrow.