They sell a device called a toilet auger designed to help clear the trapway of a toilet. If there's something caught in there, it sometimes will catch it, but if it can't get through at all, you would be certain there's an obstruction. A comb, pencil, pen, toy, etc. can easily cause the issue you are seeing. Sometimes, you have to pull the toilet if the auger isn't successful, and go at it from below.
In the meantime, make sure the siphon jet is clear. Some of the older toilets used a float on the flapper valve, and those can be small enough to get sucked into the innards of the toilet and mess things up if they ever get detached. That would likely be hard to remove, if possible.