Orange juice
E suffered really badly with constipation when she was tiny... before she was 6 weeks old.
She also had the blood on her stools, from straining or from the stool tearing the delicate skin... We were also told that, because it hurts so much, they do hold it in - which make it sit in the cavity longer, and drys out more - as you say tea, it is a vicious cycle.
We were advised by a health visitor (un-official advice, not official guidance, but she said this is how they used to treat it in neo-natal wards in Yorkhll) to give her 25ml of orange juice diluted with 100ml of boiled water.
That is obviously just for tiny babies but we have used orange juice since, to clear any problems - she has never got that bad again, because we give OJ as soon as she is any signs of constipation. Dilute half and half (or there abouts)
I really feel for both of you (((((HUGS))))))) - I can't think of anything worse than seeing your child in pain.
