water rising after flushing - can i do anything?

[jellyjelly]

My toilet has just started to rise when flushing then it goes straight down after.

Can i do anything, i dont want it to block and it is starting to smell more than normal so i have stuck product down there.

Anything else. ?

A very big plunger. I know. Ick. But it does work (wrap your arm in a couple of plastic bags first).

is there anywhere else i need to investigate?