Hi ive had a vasectomy several years ago, recently ive started getting a burning/ache sensation in my left testicle. all std tests were negative and kidney, liver, a1c tests were normal. any idea what could be going on ?

Tests should be done based on findings on exam. What did the doctor find on exam?. I do not think it is related to your surgery, Use local heat 10-15 mts three times a day and wear a good support underwear. If not better in about a week see a Urologist and make sure the area is examined. I think you will be OK

Without an examination it is impossible to give you an answer. Good Luck