I think your problem may be the refill tube off the top of the ballcock. After every flush, when the tank is refilling, there is a tube that runs to the center of the tank from the ballcock and dumps into the overflow tube attached to the flapper riser. This tube refills the water in the bowl as the tank is refilling. Flush the toilet and lift the tube out of the overflow tube, see if there is a fast stream of water going into the tube. If the water is not flowing, the tube may be clogged. If the tube is brass, its a very old type of ballcock. If its plastic its relatively new. It still clogs up once in a while. If it has, it may be time to replace the ballcock and flapper of your toilet. A very simple proceedure, requiring only a couple of tools.
Check it out.