Are these spots itchy? Any recent changes in your diet? Any other symptoms like fever or fatigue? If you suspect anything might be causing you an allergic reaction (certain foods, liquids, lotions, soaps, etc.), refrain from using it and see if you notice improvement. The water where you are travelling may also be to blame.
Hypopigmentation (the white spots) from the sun is common and generally harmless but it never hurts to get them checked out.
Signs of Melanoma are changes of color or texture in existing moles/birthmarks, or a new growth on the skin. So always keep an eye on any birthmarks you have and wear sun protection at all times. If these spots continue to pop up it is better to have it checked out and waste a day of exploring than put your health at risk, right? Besides, you'd be worrying about it for the rest of the trip anyway, and that's no fun!
Hello,
I would suggest you to get it examined from a dermatologist. Such a rash which comes on suddenly and appearing on the whole body is most likely due to an allergic reaction. The other possibility is of a viral infection.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.