As a waitress i carry heavy trays of food to customers....my wrist takes the brunt of it as it is cocked back up high carrying them. now having pain in the side of my hand near thumb. what could it be?

DeQuervain's: You may have developed DeQuervain's tenosynovitis and inflammatory condition in the tendons of the thumb. Here is a link to read more about it and some treatments. http://www.mayoclinic.org/diseases-conditions/de-quervains-tenosynovitis/basics/definition/con-20027238

Wrist pain: Probably you are starting with some carpal tunnel issues. Hyper extending you wrist while you carry those trays could cause inflammation across you wrist which would compress the median nerve. This is very common in your job. Using a wrist brace to prevent that bending helps but ultimately you need to change how you carry the trays.