Its a rare thing to have one with yr long issues but it does happen. Out of the 11 igs we have owned we have only had the one that ended up as a "display" pet and we had very little contact with him except for feeding and cage cleaning. He died at age 14 after stomach surgery but before he became ill I went 4 yrs without petting him and only moved him to go to the vest or suncage, always a battle and a towel thrown over his head.
The weather has been whacky, and warm when it shouldnt be , all over the globe, this could play a big part in prolonged season and I have heard from several ppl that this has been as especially long one.
Dont give up just yet.