Pain on left side of testicles with redness, also a red rash on face, neck and body. Mostly face. I recevied oral sex about 3 month ago, I am having sight pain in testicies area. The red rash started about a month ago. I have had all the commom STDs test

Rash. You need to see either a dermatologist of a family physician to get the proper diagnosis and or tests to find the cause and start proper treatment.
Sx's. This can't be diagnosed with the information that is available. A history, physical examination & other studies may be needed to determine cause/causes. Once accurately assessed a treatment plan can be developed.
Your . Your symptoms are concerning, and this persistent rash needs to be evaluated, as does the pain in your testicles. It was appropriate that you had std screening, and while reassuring that it is negative, i agree with your doctor that the specialist should be seen. If you have increased rash, fever, increased pain, or vomiting, then you would need to be seen immediately.