Hi Magnus. Welcome.
When I switched, it took about 2-3 weeks for my body to adjust. Nothing like your symptoms tho.. I just felt more tired than usual. I went from vegetarian to vegan. I did get worried about it tho. I lost a couple pounds (3 only) and then leveled off. I've regained that since.
I think any major dietary shift throws your body out of whack for a bit... that is probably normal. Maybenot could be onto something about the increase fiber in your diet... if you did in fact increase that substantially. Your description almost sounds like food poisoning to me, tho to my knowledge, that usually comes from meat so I don't know. The foods you listed look like you are eating very healthy.
Hope those symptoms subside for you pretty quick.. doesn't sound like fun.
Also interested in how you were able to go for that long without giving up, and were you training at the time?
Any daily caloric goals you needed to reach during the transition to veganism?
And I agree, at one point I thought about food poisoning but I really wasn't feverish or aching elsewhere. Only my stomach.
The only positive thing I have to mention is that I feel like I'm sleeping a bit better than before. I've never had any trouble with sleep before but it just feels slightly better now plus it doesn't take me as long to get out of bed in the morning as before.