If it's external, you can either get creams, or ask your doctor about it.... Sitting alot can cause Hemorrhoids, with or without constipation, it just depends on what you're doing... or how you're siting, you're probably sitting in a way that puts pressure on your anus, causing the hemorrhoid to form. But it could also be alot of reasons why it came back, if it's worrying you that much, and you're not sure what to do, i would consult with your doctor, tell him, there's no pain when passing a stool, but if you bump it, or touch it, it's painful.
I've never had External Hemorrhoids, I've had hemorrhoids before, but mine were Internal.... and i sit alot too... hemorrhoids are annoying to deal with, sometimes medications clear them up, sometimes surgery is required, it just depends on how willing you are to go with it.... But i wish you luck, and i hope you are able to find some sort of answer or relief from this....