When I was 22 weeks pregnant, I started experienced pain from time to time. I went to the hospital, and the OB/Gyn who visited me told me he knew exactly what I had, a moderate case of first time mum syndrome. And sent me home. 4 days later, I lost my baby boy.
This said @pizzanoodle , the PP has a point, we have an image in our mind of what a normal baby looks like, when the reality is they come in many shapes and sometimes even weird colours. It is. also true that some babies are really unhappy and cry a lot for no reason sometimes for weeks, months,
But we don't know . Yes abdominal distension is common in babies, but not constantly. The belly would swell after feeding and then go down and soft. If the belly stays swollen or is hard, it is a good reason to consult. A doctor should assess abdominal distension with irritability, and make the relevant questions, about how often she has bowel movement, does she have fever , losing weight, ...
Since she is so young, could she still be in the care of the hospital where she was born (no idea how UK system works) .
Take reassurance in the fact that you have seen both the GP and emergency department, so the big risks have been excluded.
Some babies cry a lot. My middle child was the unhappiest baby on earth. Cried non-stop for 8 months. Day and night, even in her sleep (and she didn't sleep much at all) . And now the happiest teenager in the world. We joke that she has already used all the tears her body could produce in the first 8 months of life. Had she been my first, she would have been a single child. She would just cry and cry and cry.