Gyn recommends backup with IUD?

Well, my first IUD lasted till 2 weeks after my first post-partum AF -
five months after I had it put in. It wandered out of position, and I
was experiencing signs of infection. We've moved, so I went to a
different ob/gyn than the one who put the IUD in. The new one tells me
that the strings were cut way too short, and that my old ob/gyn should
have been checking the position of the IUD with ultrasound every month,
then two months, then 3, then 6 . . . etc, in the first year.

I was pleased that my new ob/gyn was so thorough and takes such
precautions. She told me it's the preferred form of birth control of
her patients, and she's never had a complaint. So, when my next AF
came, I went in to get a new IUD put in. After she put it in - quickly
and painlessly - we were talking and she asked if I was still
breastfeeding. I said yes, my toddler. She made a face, as if to say,
"wow, that's a long time to be breastfeeding," and then said that by
now I was likely ovulating. I said could be, but that my cycles
continue to be very inconsistent. As she was ushering me out the door,
she said, "the breastfeeding isn't working as a contraceptive now. I
want you to use alternate protection *as if you didn't have an IUD in*
for the next SIX MONTHS, till we know for sure that it's settled in
properly." I was in a hurry, had to pick up my eldest from school, and
sort of said, "okay, thanks, by, see you in a month."

Six months? If I have to use condoms for the next six months, why did I
get this thing put in?!?

My old ob/gyn told me the IUD was effective from the moment it's put
in, and everything I've read corroborates that. I'm just totally
confused. I'll ask her to clear this up, but I just wanted to check in
here and ask if anyone else has heard advice like this after getting an
IUD put in?

TIA,
99