I mentioned in another post that your baby has very similar issues what what mine did.
A list of the things we went through - screaming all the time, wouldn't sleep, bad wind, only taking 2/3oz at a time, a lot of straining and green poo's - after seeing Hv and doctor her weight was terrible, she was 12.10 oz at 11 weeks and they weighed her again at 23 weeks and she was 13.03oz , she's dropped from the 50th to the 25th centile. although if been back and forward to the docs many times about problems, we changed milks to see if it was the milk that wasn't agreeing with her, we tried comfort milk which worked for about 3 weeks then the symptoms came back.
Anyway, after a lot of pushing and tears we were checked and she has a dairy intolerance. We are now on neocate lcp milk and started dairy free weaning 4 weeks ago and she is like a different child.
Her poo's had been green from about 5/6 weeks, we were fobbed off with colic because she screamed a lot and struggled to get her wind out the bottom end - but things came to a head when she was meant to have grown out of the colic stage and still going through it !
Go and see your doctor and ask if you can try neocate lcp xx