Why is my skateboard wobbly?

My skateboard is very wobbly and it messes me up when I'm trying to do tricks. There is always one wheel off the ground when I'm not standing on it. I've tried loosening it and tightening it to its full extent but it just won't stop being wobbly, I don't know if its my trucks being to tight on one side or something or what. I bought it off CCS and they were the ones who put it together. Any suggestions on how to fix my problem?