Hello and welcome. So, that morning nausea could have been due to the change of schedule and low blood sugar. I found out about low blood sugar in the morning after my son and sometimes myself suffer the same thing but on a more regular basis. Basically, while sleeping, we don't eat so blood sugar drops. We get up and it is low and we show it by the way of nausea. While it seems counterintuitive, when nauseated we don't feel like eating, if we force ourselves to eat a bit, normally the nausea should go away. And this may have all resulted in traveling and not having your usual routine of eating.
As to the ongoing problem now, that is hard to say. We had a parasite issue in our family after going to a farm and while we knew not to drink the water, everyone ate fruit washed in the water. Sigh. 70 people at a family reunion all got parasites. So, myself, my husband and one of my kids got it. The distinctive factor is smell. Oh my, the gas smells like nothing you have on a normal basis. I think I cleared a department store with the smell before I got rid of the parasite. Ironically though, my husband took the medicine to rid himself of it, my son tried to and took maybe half of the prescribed medicine due to intolerability and I took none as I had an infant at the time and was nursing. We all got rid of the parasite. So, they do tend to go away on their own too if it has been awhile since you traveled. A stool sample determines if you have one. I'm guessing you don't.
So, then it is back to stomach issues of rotating constipation and diarrhea. Could you have ulcerative colitis? That's a possibility. But you'd have very watery stools if that was the case and mucus. And maybe some blood. ? But this could be the situation. Or you are just getting back to normal after your trip. Or, you've developed IBS. Ha, I'm not too helpful there. Sorry. But it is hard to say. I would work on the constipation first. Something like drinking a glass of grape juice a day may really help
If you begin to lose weight, definitely see your doctor now. But otherwise, wait to see if it clears up but don't wait too long. Since you have a history of stomach issues including gluten sensitivity and you traveled where all bets are off food wise as much as you try to control it, you may just have aggravated things and it will go back to normal.