I'm currently on holiday in Barbados and after sitting out by the pool for 60 minutes I have got really bad sunburn. As a rule I don't burn and didn't when I went to the Dominican Republic a couple of years ago. Could Metforim be the reason??
Barbados is materially south of the Dom Rep.
I spend a lot of time in that general area of the world, but must respect the sun significantly more since we relocated a little south (not nearly as much as the Dom > Barbados distance). If your 60 minutes was near the beginning of your holiday, I would say that was quite a hit.
If find in the tropical climate, I get just as brown sitting in the shade, taking reflected rays as I might do trying to juggle and sunbathing.
I hope your recovery will be quick. Drink lots of fluid and apply copious aloe vera gel if you can locate it. I imagine you should be able to find local Aloe very easily.