Advice!! My 8 week old doesnt drink much?!

My little girl is 8 weeks old for the 1st 4 weeks of life she thrived off cow and gate gaining weight and coming along lovely! Until she had bad colic and became constipated we were advised by health visitir to use c&g comfort, this did not help and she cried takin her bottle having green runny poo (sorry to b graphic)We then took to docs shes only takin 2oz every 4hours and cries takin milk where we were then told intolerance 2 dairy and put on wysoy milk! A week later she still no better not drinking and not putting on weight but not losing either! shes constipated again n doesnt seem To enjoy her feeds! Now theyve taken us off the soya telling us we shouldnt of been goven this and back on the normal milk which weve gone to Aptimel to try but with gaviscon which they have prescribed saying she has acid reflux? ino we have to persevre with this milk but shes has 3oz then next feed maybe 1pz then sleeps for 4 hours then has 2oz shes just crying through her feed and its making us so upset and run down! Weve changed bottles, teats, milk, used gripe and infacol! She still only takin 2oz but cries through that! She seems sleepy but still a happy baby? Im really worried shes not getting enough and dont no wat next steps to take?