Did you drink all thirteen pounds at once?! I once obtained 13 pounds of San Pedro from the Amazon river basin, and ended up drinking about 7 pounds of it over a few hours (which is a SHITLOAD of cactus). I didn't get any effects, which was one of the many times that San Pedro didn't work for me.
I split it with one other person. It was an iso extraction so I didn't have to eat much material.