Hi K.,
Check behind the cloth of the child seat seat (behind and under where the child sits). There may be a strap or LATCH end (or toy) that is poking into the child's back or bottom and is making the child uncomfortable in the seat.
However, my primary concern is safety. I want to address a few issues from the list:
1. The harness should be tight enough so you cannot pinch either harness strap (like you would try to shorten it -- NOT like you would try to make it more narrow). You should almost be able to pinch it, but not quite. The "one or two fingers under the strap" method is outdated. If the harness is too loose, the child may be ejected from the seat. Child seats are primarily SAFETY seats, not "comfort" seats. By the way, the harness clip is always at armpit level.
2. Don't use mirrors that attach to the auto headrest in front of an infant seat. Two reasons. Parenting and driving should be done separately. If you're driving and need to parent, pull off the road and do it safely. Was it this list where I read something about a mom that reached back to a child and rolled the vehicle?
Second, mirrors are not tested to resist crash forces. If the mirror weighs one pound, at 30 mph the mirror weighs 30 pounds. And guess where it will fly if it fails in a crash? Right into your child's face.
3. Someone mentioned using a noodle. For a rear-facing seat, a noodle (or tightly rolled towel) may be used to increase the angle of recline. An infant should be reclined at about 30 to 45 degrees, but no more. If the infant sits too tall, the head may flop forward and potentially block the airway. Too far back and the child's head (being the heaviest part of an infant's body) may be pulled in a crash and cause damage to the spine.
4. Keep your child rear-facing as long as possible! "One-year and 20 pounds" is an absolute minimum and is not best practice. With some infant seats now rated up to 30 pounds and "convertible" seats (may be installed rear or forward-facing) now up to 35 pounds rear-facing, why would anyone want to degrade their child's safety by turning them forward facing too soon.
Yes, I know: "My baby's legs are scrunched up against the seat back." My answer: "Legs and feet heal, brains and spines do not."
Because I care,
-- M. Cohen
Passionate Child Passenger Safety Instructor I-575114
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Loving Step-Father of Melissa Monique 1980-2002
Loving Grandfather of Alec Jaye 2000-2002
"Again this year, Alec and his mommy won't be going to Grandma's house for the holidays."