Okay, it could be a number of things.
Rest assured you will come to the bottom of this, you'll get a solution, things will go perfectly for awhile then voila.....a new issue.
Doubt she could be teething yet but she could be getting ready. My child
did the pre-teething at about 4 mos. It went on for abt 2 mos then he
actually teethed.
Could it be a reaction to your milk/formula? If she gets formula, she could
have an allergic reaction. Ask your dr then possibly change her formula
if she's formula -fed.
Sometimes babies go through stages. When mine was little, we went
thru several stages at that age where he would sleep better in his car
seat carrier, swing or stroller. At that point, if he was fussy, I'd put him
in his swing or stroller & walk him then if he fell asleep, I'd leave him in
there to take his nap.
Work "WITH" what you have and what work for YOUR baby.
It will all work out AND constantly change. Hang in there, best of luck &
roll with all the changes trying new things!
Edit: If it is early teething, rub baby orajel on her gums just in case. Then
when it's more serious teething, give baby Tylenol (Baby Motrin for the
molars).