In Pattaya central area, there are several shops which sells protein powder and other nutrition. But most of them are relatively expensive.
My most recommended way to buy protein at Pattaya is to use online shop called “Pattayawhey”(http://www.pattayawhey.com/).
The price is the most competitive in Pattaya as far as I know, and they can deliver to your home or hotel in Pattaya for free. When I have ordered protein at the website, the staff always delivers within 1 or 2 days. They will phone call you before they deliver, so it is really comvinient and reliable. I have ordered so many times at the site before, no accident and no problem at all so far.