Hey Vinay, The month of May marks the beginning of monsoon in Thailand, so you may find occasional showers while there. This may upset your sight-seeing schedule. On the positive side however, prices are significantly slashed down during this time since it is not peak tourist season. Moreover, there will be less crowd so can enjoy the beauty of Thailand in peace. I would suggest that you check the weather forecast and plan the places you visit in Thailand accordingly. This 15 day itinerary will help you plan your trip: https://www.tripoto.com/trip/the-only-15-day-itinerary-to-thailand-that-you-need-5b28bdff4af55