In general, whenever you notice new or concerning changes in your skin, the best thing to do is to see a dermatologist
for closer evaluation. If you have a relationship with a dermatologist already, you should hopefully be able to be seen quickly by someone in the same group. Generally sun exposure does not cause immediate skin changes such as you describe. So called 'sun spots' caused by sun damage to the skin typically take years to develop, not the very rapid change you describe. For this reason, it is certainly possible that there is no association between the skin changes and the sun exposure--you may have a skin issue which is entirely unrelated. The most useful thing about seeing a dermatologist right away is that many, if not most, skin issues are diagnosed based on appearance of the lesions. The list of possibilities depends upon the color, size, location, pattern, whether or not the lesion is indurated or has palpable elevation, etc. A dermatologist is the best specialist to be able to put together this exam with your known history to try and help suggest a diagnosis. In addition, it will also be helpful to know if you have experienced any other new symptoms as well as your general health background.