jnicole, You either need to repair the ballcock (with bulb) or replace it. Depending on the brand of the toilet you may be able to replace it with a fluidmaster ballcock available everywhere but some toilets require that you use the original ballcock. I have most of the common toilet parts breakdowns on our web site that may be of help.
Why not have a real plumber look at it instead of guessing. The running water could be a defective douglas valve OR a corroded over fow tube or a refill tube set to low Or a bad disc (american standard) flapper Or a bad tank bulb or flapper.