Just Constipatied?

Ok so my Husky mix who 9 this year has been having some constipation issues recently ( She was constipatied a few months back and a suppository at the vet fixed it ) She has had some health problems in her life (pancreatitis , anal glands not draining)  This lot started just over a week ago took her to the vet again gave her a suppository and some liquid laxative and said if it hadn't help and she was still struggling to poo to bring her back we did the liquid laxative as directed and she seemed fine untill q few days later she wanted to go out every 20 mins to an hour all night long. Took her back to the vet (checked her again and the poo was soft ) they suggested an untrasound and blood tests (preformed 31\7) All tests came back fine and nothing on the ultrasound. The vet suggested we start giving her a scoop of fiber supplement on her food at night and using the oral laxative once every few weeks. Today 1\8 she has now started yelping while pooing its dark outside so i cant see her poo but i'm at a loss as to what it could be we plan to contact the vet again. Shes been a picky eater since she was a puppy but her diet consists of chicken breast or chicken mince ( on a low fat diet because of the pancreatitis )

Hello!  To state the obvious, it sounds as though your husky is having a problem with food advancing along the gut.   Reasons for this may include a narrowing of the gut (caused by some partial blockage for example a tumour or large organ pushing upon it) or a widening of the gut, for example by a reduction in nerve tone to the gut wall. An ultrasound might have picked up some of the causes of such problems, but didn't in this case so it sounds as though further tests may be needed. Has your vet exhausted all their tests?  It may be worth asking whether a Barium meal would be helpful in this case, for example, but these are difficult to perform.  It may be possible that referral to a specialist is needed to provide more information.   Questions like:. What have you rules out?   And what could it still be?  And How can we rule this out?  May be useful. Best of luck.