The only human-infecting intestinal roundworm of that size is Ascaris lumbricoides. A mature female Ascaris is roughly about the diameter and length of a wooden pencil. Menbendazole and albendazole are the standard treatments for that, so you may already have done the right thing. To be sure of being rid of the infection, though, requires microscopic stool examination to see if one is still passing Ascaris eggs (see third photo). You would need to see a doctor about that, who would provide instructions and an appropriate carton for specimen collection. It’s not a highly dangerous parasite unless it accumulates in such numbers as to cause intestinal obstruction, as often happens in children in endemic areas. Intestinal gangrene and appendicitis are sometimes triggered by healthy infections.
Ascaris is usually contracted from food or soil contaminated with human stool, so if you are or were infected, it may mean you have an environmental exposure somewhere to contamination with human sewage. That can range from poor plumbing in anything from private homes to luxury hotels, to raw sewage being dumped someplace you have exposure to (from ponds to farmyards), to poor sanitation in restaurants you visit (even from unwashed hands of employees who prepare a salad or serve foods to one’s table), to exposure in foreign travel.
Photos: (1) A mass of Ascaris removed from one child. (2) Female Ascaris on the left, male on the right; the male is a bit smaller and has a more curved or curled tail end. (3) A female shown for size, and Ascaris eggs in the two photomicrographs.