I got very sleepy after the infusion which nobody else seemed to have either and tired for 3 days.
Radiotherapy can definitely cause issues with your gut if it is close by.
I don't recall issues with taste from herceptin but after finishing chemo and 2 months on was on optifast trying to drop all the weight I'd put on during chemo. Everything tasted amazing on 800cals a day.
I wonder if your other medications could be contributing?
Just be aware you are exhausted from treatment and this is a set back. You are over halfway now ...there is light at the end of the treatment tunnel..