I have a terrible problem with lying to my parents
Why do you lie to them?
It's not fair to me to always have to tell the truth.
You shouldn't lie to your parents like that. You need to tell them the truth, not just pretend to do so.
Why should I? I'm an adult and they need to stop pressuring me.
It's true that people shouldn't be too invasive, even parents, however that is not an excuse for lying.  Telling lies will only cause more problems down the line when they find out, or you mix up the falsehoods, so it is best to just be honest from now on.  You'll find it gets easier with time.