3 month old daughter feedings..

Lindsay • Just a small town girl with big dreams and hopefully a little one soon :)
My daughter will be 3mo old on Friday. 
She has progressed normally as far as feeding goes. She has recently been eating as much as 7-8oz in a feeding, every 4 hours (she is formula fed). A few times, now, she has stopped eating at around 5-6oz and then she is done. 
I suspect a growth spurt has ended but I'm a FTM so I can't be sure... 
This morning worried me because she would eat but she would cry and be fussy while eating and then stopped at 5oz. Then she fell asleep and has been asleep for about 20 minutes, now. 
We live in Michigan and the weather has been wonky- so her allergies (thanks mom!) have been acting up, as have my own. So she's been extra mucousy.
It seemed that this morning the mucous was getting stuck in the back of her throat and she was having trouble eating because of it. 
I'm just nervous because SIDS scares the hell out of me.