How many times can i take mebendazole, if i already took 3x1 dose for the prescription. (like weeks after) but i still have worm infection?

No limit, but: If the treatment is not working,the assumption that you have pin worms may be wrong. Peri-anal itching is common to many food intolerance and other problems. It might be worth a real PW test to see if they are there. Mebendazole is a simple neuro-toxin to the worm and is given for prolonged periods at higher doses to treat other types of infections.