When you change from a regular diet to a vegetarian or vegan diet your body does need to adjust. The micro organisms in your guts have to build up a new balance. You need different bacteries for digesting meat then for veggies.
I changed very slow from regular to vegetarian. It took me at least a year. And after being vegetarian for one or two years or so I moved on to vegan. That is probably why I didn't experience any problems in my body.
The health benefits were very obvious for me but I also had a lot of work in changing my perception about plant based food. I used to see it as kind of inferior in several ways. So with such perceptions it's more difficult to make the change.
I am very happy that I persisted though. My health and well being have both improved.
Scientific research supports the notion that plant based food increases your well being.