Oh no don't go front facing, some states wont even let you do it till 2 yrs now I believe.
Is she in pain...needs an adjustment from a Chiropractor
She is a new mobil baby she might not like being contained. Can you blame her...all these new things she can get to now more then likely.
You could try a rear facing convertable but more then likely you will still have this issue. I highly suggest not moving to a front facing. If you have ever seen a child go through a car accident even at 35mph you would know why I say this. She is a fragile baby. A little fussing isn't going to hurt her but the chances of injury in a front facing position being fatal at this age is high.
I highly, highly doubt it is the car seat.
PS, my sweet daughter is almost 8 months old and close to 19lbs and she is as confortable as can be in her seat that goes to 22lbs, sure she was fussy for a while after getting more mobil but now is happy...she's got her days