Unfortunately, gluten can take 3 months or more to get out of the body - so while you may feel better sooner than that, you may not know the impact of gluten on your body until you have been gluten free for a while longer.
With the detoxing issues many of us have, it can take even longer. I'm just now reaching the 3 month mark - this week! - which is why I'm missing my gluten foods so much now!! LOL!!
I feel like I've been fortunate to not have a wheat allergy- and when I did a trail of wheat, I had no symptoms at all...... but, I've determined that since I'm already gluten free, I'm not even going to try gluten (knowingly) at least until my adrenals heal and my tick-borne infections have healed again. Too hard to go gluten free to want to risk having to do it again!!
But I still don't blame you for having that 1/2 slice of pizza!!!