BF mommas HELP!

I'll be calling monday when my lactation consultant gets back from vacation but until then I need some serious help!
Lately when nursing Kenzie she never seems to get satisfied... She'll go for half an hour (switching sides every 15 min) but even after being on both sides she will continuously pull off and begin to fuss. I've tried burping her when she fusses but no such luck. She continues to root around. I just feel so bad as she will continue to pull off and fuss/cry.
She also gets hungry a lot sooner now than she had been getting before... She used to go about an hour and a half to two hours before and now it's anywhere from five minutes to half an hour... 
I would assume that was from cluster feeding however when I weighed her today her weight was back under her birth weight...
Should I start supplementing with formula... Or will I be fine until Monday... 
I'm just worried about her...