What is the best treatment for sun poisoning spots and what can u do if you have to work in the sun?

Sunscreen: "sun poisoning" is just severe sunburn. It should be treated with cool washcloths applied as often as feasible, and Ibuprofen or a similar anti-inflammatory for the pain and inflammation. You can prevent it by applying a good broad-spectrum sunscreen lotion every day, and reapplying it frequently while you are working in the sun.

Sun protection: In addition to the suggestion by Dr. E. you should consider physical barriers to avoid sun exposure, e.g. wide brimmed hat, clothing, umbrella etc. Make sure to stay hydrated to avoid other complication of working outside in the sun.