Dr Green will be coming up if he has turn out access (obviously has its own complications). Does he box walk or any other anxiety type behaviours?
Re- worming, encysted red worm can be persistent. I had a mare who was very colicky despite being on a 4x year worm programme. I had moved her onto Equimax (Ivermectin based) as she was lactating. After this had gone on for months, my vet did blood tests which were 'elevated' and he recommended 5 daily dose of double strangth panacur (liquid cheaper than the sachets and many folks use the cattle/sheep which is cheaper again, but not licensed obviously

). Followed that up with Equest, which is what she had the first year since I owned her (think its moxedectin?) about 6 weeks later at the same time as the other horses. If a problem suspected then best to dose twice for encysted with alternate products ie the Panacur (fenbandazole) then Equest (moxedectin) (or vice versa). Usually Nov/Dec and Feb/March depending on mildness/frosts.
Its also the start of the grazing season so time for tapeworm dosing as well.
Neither of these show up in worm counts.
(apologies if drug names spelt wrong)