Water not filling in toilet. Can be flushed once and then have to wait for it to fill to its very small level. Tank seems full. Also in the same bathroom used drano 3 times. Clears for a few days and clogs up again. What can be wrong??

First remove the tank lid and make sure that the refill tube, that little black tube from the fill valve to the overflow pipe, is pointed into the overflow pipe.
If so flush the toilet and make sure that there is a good stream of water from the refill tube into the overflow pipe.