My bathtub has the old fashioned compression faucet and has been leaking for more than two years already. I decided to try to stop the leak and only made it worse. After taking off the handles I pressed down on the knob and realized that the leaking stopped completely and decided maybe it's loose I should just hammer it down to tighten it. It only made it 5 times worse! I ended up replacing the knob thinking that it would be fixed but it's the same. And I noticed that when I had turned off the water supply to the house that it water continued to flow. I'm thinking that it's the tubing. Do I really have to get a proffessional to take a look at it or is it something I can fix myself and what's the problem?? Please help me out :/

From your post I assume that you have a two handled tub valve, (see image)
If you haven't damaged it beyond repair by beating on it you should replace the washers. Shut the water off and open up the valve. Replace the old worn washers. Now take your fingernail and run it around the seats. If you feel, any nicks or rough spots the seats must be replaced as well.
Good luck, Tom