Screaming in pain but watery poo?

[Twitchett22]

My 3 week old is FF and poos usually every feed. Her poos have been yellow and seedy with some mucus (midwife said this was all normal) and over the last few days they have changed to a more pastey peanut butter type texture. But since yesterday she has been straining and screaming while she's pushing, she looks like she's in lots of pain and only maybe 2 poos a day so i put it down to constipation. However today she did a massive poo, yellow and seedy still but it was watery. She's still upset when she's straining even after getting all that out, but why would she be in so much pain pushing when the poo is watery not hard?!
Im seeing the HV tomorrow so will ask but just wondered if anyone else has had this, its awful to see her so distressed

DS got upset when pooing around this age... they have to learn to use the muscles and he didn't like the sensation. He sometimes screamed for an hour before, pooed and all was ok again. Lasted a few weeks then he calmed down. Baby massage, leg cycling and a warm bath may help. But definitely get your HV to check there isn't something else going on.
Breast fed babies can go up to 10 days without pooing after a few weeks... 2 poos a day at 3 weeks sounds normal to me... constipated baby poo looks like rabbit droppings

Tummy cramps with a watery poo can be stronger than normal and it's a very new sensation to a baby. he doesn't know it's ever going to stop!

Thanks for the replies, she pooed on cue at baby clinic so HV saw and said it looked completely normal and her screaming is her getting used to the sensation of needing to push. Hoping it will pass soon its horrible to see!