Thanks for your question. From your descriptions, it is evident that your condition is something caused by Benign disorder. Moreover, from your words probable diagnose of your issue is that of varicocele or epididymitis. Varicocele is caused when testicular valves become incompetent and blood which is given to left testicle get collected there itself. This is the reason of what causes your left testicle a little bit heavy. Inflamed epididymis or epididymitis also have similar signs or symptoms which also have pain. It is better not to examine your testicles by yourself. Let your doctor do it if it is possible. A urologist will be expert in doing all these. Testicular ultrasound and urinalysis are helpful in diagnosing problems. Good luck.