Problems with toilet weak flush?

Toilet was working fine then all of a sudden it is flushing weak and the water sputters at the end like it is clogged. The bowl fills back up, but not as much as it should (I think). The waste goes down (just trying single toilet paper for now) but the flush seems "weak". Teenager flushed tampon the other day however we have plunged and nothing comes up... If waste is going down could there still be a blockage? What would cause a weak flush all of a sudden?