Hi Wanji,Welcome to the Healing Well 
Wrapped Club! The shoulder pain is pretty universal. It's referred pain from irritation of the diaphragm in conjunction with the gas they pumped into you. It is extremely painful and annoying, I know. I was told by a night nurse in the hospital that I should walk as much as possible, and that was the best advise ever. I found the more I walked the less my shoulder hurt. I suggest that you walk as much as you possibly can manage as often during the day as you can.
I know of others here who had a lot of trouble with diarrhea while on a liquid diet. Joy (couchtater) always says, "Liquid in, liquid out". Also there's something called "dumping" that can occur after stomach surgery in which the stomach empties too quickly and that causes diarrhea as well. I had it intermittently during my recovery. I could always tell it was coming when I heard loud gurgling in my stomach. If that's happening to you, an anti-dumping diet may be helpful. Here's a link to some information:
http://uvahealth.com/services/digestive-health-1/images-and-docs/dumping-syndrome.pdf/view
Obviously the diet references are beyond what you can eat right now, but take note of the effects of sweets as a trigger.
You're in the roughest part of your recovery. Hang in there! It gets better. I don't know how much you've explored the forum, but in case you haven't seen it, here's my early recovery journal:
https://www.healingwell.com/community/default.aspx?f=45&m=2183443
(Ignore the references to asthma issues...the other things I experienced are typical.)
We're here to offer support and share our own experience with our own recoveries. I had the surgery four years ago, so I remember it well. Be sure to continue asking any questions that come to mind. Best wishes!
Happy healing!
Denise