Aww hun i am not 100% sure but it sounds as though your LO might have a belly ache, the arching of the back and pulling up of legs def suggests to me it's something to do with her tummy.

There are quite a few things you can try to assist with releasing that wind so it doesn't build up, i'm sure the ladies can make some good suggestions for you, i had to use infacol with DD1 for a while.. even though she was a good burper she was holding a lot in.

Does she take a dummy, sometimes the sucking action can help release some air aswell.

BF babies can go days without a bowel movement, as long as she has plenty of wet nappies and the dirty ones aren't a strange color, are they still that mustard yellow?

Sorry prob not much help, if your really worried it doesn't hurt to ask a MCHN or your GP.

My DD2 is 4mths aswell, when was your daughter born, feel free to check out the baby buddies threads and join in with people with bubs your age.... this is the link to jan 1-15th thread https://www.bellybelly.com.au/forums...-2010-2-a.html