ADHD burnout -work

Please help. I have been working full time for around 2 months I graduated from uni last year. I am doing my pre reg in a pharmacy . I let NHS know that I would want to do less than 40 hours as I know I will burnout . They told me if it’s still full time (35-40 hours) I should be able to discuss this with my employer. When I told him he just thought I was being lazy and I think he doesn’t believe this condition is even real lol but in a nice way he told me no. He told me he can not do much until another staff member joins in October. I let NHS know this and they told me he also needs to think about his business needs and maybe just wait till then.
I’m really struggling and I have lost the will to live . I already struggle to look after myself and now I have stopped completely. I have taken today off and told him I don’t feel well and I feel exhausted. He said ‘you don’t feel well and feel exhausted okay that’s fine but we need to have a chat next week. ‘