Why didn't I tan in Thailand?

I went to Thailand from May to June and i hardly tanned despite sunbathing most days when the sun was blazing in temps of 34. I went out there with a moderate tan from sunbeds. I normally have no problem tanning so why did i not go any darker? Even my stomach which normally goes super dark didn't respond! It was easy to go red but the red never turned to brown like it normally does! What's going on? Anyone know?