I was the same as Meaghan. I found the diet difficult when I was younger. I did not like drinking my formula, and I thought writing down what I ate on a daily basis was too much of a hassle. Today I see PKU as another part of my life. Everybody has something, and PKU is just what we have.
I guess you just have to find something to motivate you to follow your diet. For me I decided to get back on track when I started seeing a new doctor and dietitian. In a way I felt like I was being given a chance to start over, and I was determined to prove to my new doctor and dietitian that I could control my diet. I did not want them to see me as the child who did whatever she wanted when she wanted like my previous doctor and dietition did.
Here's my suggestion: figure out what makes the diet hard for you. For some people it's the formula. Other people just don't like the taste of the low protein foods etc. Once you know why the diet is hard for you speak with your doctor or dietitian, or let everyone here know, and I am sure we can all help.