I agree with you re: poor nutrition at the hospital. Personally, if I'm ever hospitalized, I'm having friends or family bring me stuff from home to eat. I suggest the same to patients. That said, a lot of people have atrocious eating habits at home, as well.
Re: other issues, I'm not entirely sure what you suggest be changed. Yes, narcotics can constipate you, but that's why people get put on a bowel routine when they are admitted. Inactivity doesn't do much to help with constipation, either. You can't just not give people pain meds.
Thrush is not treated with an antibiotic, it's treated with an antifungal. Regarding non-pharmaceutical remedies, I think most of us have seen enough self-treatments gone bad to insist on the proper treatment being given. I personally don't care if a patient refuses their antifungal and wants a probiotic, I just don't want them to turn around and blame ME for their thrush not resolving 2 days later and claiming I wouldn't give them the antifungal. I understand you haven't been in the field long and let me tell you, people are manipulative and are happy to throw you under the bus. I had a guy refuse to fill his Rx meds for BP/dyslipidemia because his chiropractor told him not to (don't even get me started here) and subsequently have a heart attack, then INSIST that I never gave him a prescription for them and it's all MY fault he had a heart attack. Good thing I had documented everything during our visit before.
Regarding broad spectrum antibiotics - that's usually what people get started on and then it's stepped down to a more appropriate one when the cultures/susceptibility are back. You don't want someone to get sepsis and die because they ended up growing an exotic bug and you thought Vancomycin or a 3rd gen cephalosporin was overkill.