For the most part, no penetration, no STD. No penetrative encounters are considered "safe" with the possible exception of herpes or syphilis, either of which should lead to a lesion and certainly not to the burning sensation you describe. Furthermore, nausea, vomiting, diarrhea? - no way from the exposure you describe. Remember, you were in Mexico from which many return with nausea, vomiting and diarrhea. As for your specific questions:
1. Symptoms of most STDs typically occur within a few days, sometimes as soon as 2-3 days after exposure. The problem is that your symptoms are not suggestive of STD.
3. Makes it still less likely this is an STD for which symptoms tend to be most prominent first thing upon wakening.
I'm not sure what is going on here. That it is manifest primarily as symptoms without visible abnormalities makes it possible to be a consequence of increased vigilance combined with anxiety. I would ask your health care provider or a dermatologist to evaluate. This however is NOT an STD. EWH
I just got back from Mexico (literally on Thursday) and am having the same problem! I learned I had a urinary tract infection this morning. My doctor said it was probably from using the tampons I bought down there, but it could really be anything (the soap, water, toilet paper, etc) since they are not as sterile down there.
You can go to your doctor and get some antibiotics and it will go away, but you should also drink lots and lots of water (our good american water, yay) to flush it out. There is an over the counter medication called AZO that numbs your urethra and turns your pee bright orange. This makes peeing a lot more comfortable while you are treating it.