Longer strings during period? Is this normal??

I had the Paragard IUD inserted back in April and after two months it started expelling, my doctor recommended putting another one in thinking my body hasn't adjusted to the new one. 
I have been paranoid and checking the strings constantly, and during my period, it feels like the strings are long. 
Is it normal for the strings to be long during your period then move back in place afterwards? 
- Really concerned