what do you mean by no invitation for 3 years? That you have not received acknowledgment of receipt? Or you mean you have not heard updates since then? You need to order GCMS notes and also try involve your MP to get your file moving - 3 years is a long time and the more you wait the more age-related health issues will emerge, which may warrant asking for medical exemption later as the agent may try to argue that they will be burden on health system. Whether you go with lawyer or yourself is up to you. My lawyers have all been incompetent sloppy individuals that ripped me off fortune and lost all applications and appeals, but others here have been more lucky.