Well you dont suffer from PKU, if u had PKU and was untreated till this day i would say you wouldnt be on here looking for questions you would be severely brain damaged and several other disabilities.
However i do agree maybe your allergic to some foods!
While us Pku'ers are on a very low Protein diet we also take a formula which gives us all the amino acids, minerals and vitamins that we are missing from normal foods, we can drink this upto 3-4 times a day! Also we have special Low protein foods which we get on prescription which most are high in calories and everything balances out! its all a bit hard to understand if u dont suffer PKU.
If i was you tho i would listen to your doctors orders as he knows best and you could become ill!