Getting frustrated is only going to make things worse. I would suggest taking a break from actively trying to induce lucid dreams for a week or two. Sometimes a fresh start is all you need. And many times, when you do take a break, you'll find that a LD comes when you least expect it.

Also, when you are trying, are you sticking with the same method for a while, or are you jumping around from one method to another? It's a good idea to stick with one method for a week or two before giving up and moving on to something else.