Hi there, it’s sounds like you’re having a really rough time.
Sorry if this is a bit late replying to your post, but I’ve not been feeling in a headspace to join in the forum until recently. I was offered Neratinib following previous treatments of wide excision, chemo
Plus Herceptin, and radiotherapy. Am on ibandronic acid and anastrazole daily as I am positive for everything 
I was really suffering with fatigue for a few months after radio, but it gradually improved. Just as I thought I’d finished the trips to hospital, I was offered Neratinib… I decided to try it and the first month -6weeks was horrible, terrible diarrhoea and no real warning other than lots of gurgling! There are other things that come and go plus it can make you a bit immunocompromised. My nails are terrible and my poor mucus membrane in my nostrils are so sore that they have little nose bleeds. I had the dose reduced by a tiny amount and I still take loperamide to help with diarrhoea. Now 3/4 of the year gone and I am on count down to getting away on a holiday!
Although they may push for you to start it asap, in the guidance it does say to start within a year of having Herceptin. So maybe you need a little recovery time? I didn’t as knew I wouldn’t want to if I had a break. The nurses may be able to advise on this, but may also depend on your hospital policy. Good luck x