I had unprotected sex with a man last month. I usually take PrEP 2-1-1 rather than daily PrEP but that night I vomited a small amount about an hour after I took the two pills of Truvada due to an upset stomach. I had unprotected sex with another man 8 hours later, having forgotten that I'd possibly vomited the medication.

Welcome to the Forum.  Thanks for your questions.  I'll be glad to comment.  About an hour following the first to tablets of your PrEP on Demand, some of the medication you had taken would have been absorbed from your stomach even before you vomited- possibly most of it although absorption varies from person to person.  Your two subsequent medication doses added to the protective effect.  Your 30 day test results are further strong, but not perfect evidence that you did not get HIV from the encounters you describe.  After all, remember, not only did you take the PrEP but you do not know that your partners had untreated HIV (statistically unlikely) and even if one was, most single encounters to not lead to infection.  Even if one of your partners were infected and without PrEP there would be a less than 1% chance you were infected ---