Bearded Dragon ate onion twice in a row, please help.

So, I was recently feeding my Beardie some pre made diced veggies my father made, but I didn't realize there was some bits of onion in it, so he ate this one day, (I know he probably did eat some of the onion, at this time I didn't know he did.) So again the second day I put the rest of the veggies in his cage to realize there's onion in it. I know he probably did eat some of it but I took it out immediatly, he sempt fine and was acting pretty normal. I looked up and it said its okay if he ate a little bit; which he probably only consumed a small amount.
Can someone help though? He ate it twice in a row, not in big amounts though; maybe only a couple small pieces, but i'm worried he could get sick or possibly pass away from it? What affects can onion have on my beardie if he eats too much? I've read that it will probably be fine, but i still am paranoid. Sorry if this was irresponsible, its the last time i'm letting my dad make him veggies, I dont think he realized he couldn't eat onion.

If only a few small pieces , will most likely will be OK, just keep on an on him.

Thanks, but heres an update
He was acting pretty normal the entire day so I was kind of relieved.
But later in the day he ended up having some diarrhea, and he got up onto his basking rock with his beard completely black and he just is sitting there with his eyes closed. Is this because of the diarrhea and he doesn't feel good or is it because he's sick from the onion? He ate lettuce in his chopped veggies as well so that could be a problem, either way he's closing his eyes on his rock and when I tried to pet him on his head he ended up jumping back from his rock and he still has his eyes closed.
Can someone tell me what most likely is making him do this? Also can someone tell me what affects can the onion have on him? WIll it make him sick?

Another update, he seems fine now; I think this is because he didn't feel good from the diarrhea, can someone tell me what I should watch out for though? What symptoms will he start showing from being sick because of the onion?