Water is good, better than nothing. It took me 7 weeks to drink anything post radiation treatment, and that was only a sip. I think I started out with chicken broth, egg drop soup, chicken broth with pastina, worked from there, and can eat everything by mouth now, but more treatments set me back a while, comes back, and so on. I would watch others eat, watched the food channel, read cookbooks, torture lol, but one day I just got up and started to eat, I coudn't take it anymore...baby bites.
Oxycodone makes me vomit. Constipation can cause nausea, vomiting too.