Since this morning my 19 day old dd has been crying and wanting to feed constantly all day. I'm concerned as she usually feeds every 3 hours or so for around 30-40 mins (she is breast fed) and will sleep in between when I put her down.
Today she will only latch on for around 10-20 mins on and off then doesn't seem interested in feeding any more. I will burp her then put her down to sleep and she will start crying and rooting again after a few minutes. I've tried holding/rocking her etc to settle her which usually works but she keeps screaming the house down and in the short time she does settle, she will let out the occasional cry 
She's still having plenty of wet/dirty nappies and isn't showing the usual symptoms of when she's got wind, and I can't for the life of me work out what's wrong with her.
Any ideas? The only thing we have done differently is OH gave her a small feed of formula last night for the first time as I was absolutely shattered and was desperate for some sleep (we usually give her expressed milk when he feeds her but we didn't have any stashed). Could this have caused any problems? I've done research on combi feeding before so I'm not really beating myself up about her having the occasional formula feed, but obviously I won't do it again if it's upsetting her in some way!