Insomnia from shift work

I made a reasonable adjustments request to my employer to try and get more fixed hours instead of working shift work as doing very irregular hours is having a detrimental impact on my health and wellbeing. My employer has refused to do it dispite doing it for other colleagues. I've been told I can't as I don't have children  So I shouldn't be asking for fixed working hours. I feel like I can't get into a good routine with my job and reslly feeling the struggle of it. 

Any advice?