Parasite infection. Using medicines?

I went to a araku valley tour where I have played in pond and unfortunately some amount of water has entered into my mouth and I have drunk it. After one week I found white seed like specs coming from my stool and symptoms like diarrhea bloating fatigue and nausea. Immediately I have Google and known it might be a parasite infection giardiasis or tape worms or pin worms. Consulted doctor in Delhi given medicines for above symptoms. The medicines were 1.veloz d 2.ornicef 3.zybend(single dose) After these medicines within one day the problem has gone. Given for 5 days But now I feel I am getting some times anal itching. How long should I continue these medicines?? Does parasite infection is dangerous?? Will it occur again if I stop using medicines??