You have actually pointed out the 2 main causes of your condition already, plus I'm amazed you can stand for 7 hours per day in your job! Unfortunately, prolonged standing and lifting heavy weights also aggravates your hemorrhoids as it constantly places your upper body weight pressure onto your hemorrhoids. (The same goes for prolonged sitting)
You have to moderate between standing and sitting down every now and then, and if worst come to worst, you should tell your supervisor about your condition and allow you to alternate between standing and sitting in your job.
Your case is fairly serious actually, and you definitely shouldn't ignore your hemorrhoids because if you carry on with your living habits the way you do now, it will only worsen. Here are some tips to cure hemroids which you may find useful. All the best.