That is a difficult situation and one that I was in myself for many years. After a lot of years of dealing with ITP and the treatments, I was diagnosed with Lupus. For seven years, I struggled with work...working through lunches and staying late. I'd go home and fall on the couch. My home life suffered and forget any sort of social life. There wasn't one. I kept plugging away because I had to keep working to keep my health insurance. There wasn't any choice.
I always felt that if the time came when I couldn't do my job properly, I should step aside and let my employer hire someone who could. So I kept pushing myself to do the best job possible. It took a major toll on my body and my health issues became much worse. Two years ago, I had to quit because I just couldn't do it any more. It took me about nine months to get my ducks in a row with health insurance and money, but I did it.
The point is that when things get bad like that, you need to consider some changes. There was a woman here a few years ago who had a similar situation as you and she was unable to keep up with her current job duties. She fretted and didn't know what to do; she was a basket case. In the end, she got a different job and was very happy with the changes. It turned out better than she could have ever expected.
BTW - Have you had a good work-up lately as far as blood work? Many people with ITP also have other health issues, sometimes simple ones like vitamin deficiencies that can cause fatigue. Sometimes it's a thyroid problem or other autoimmune issue. ITP could be the cause of fatigue but I wouldn't just go on that assumption. It can't hurt to look at other possibilities. I've been surprised quite a few times by blood work that revealed low vitamin levels, especially because I take some good OTC's!