If your your father is a carrier this means he has one normal gene and one PKU gene. You have to have two PKU genes in order to have PKU, one from mom and one from dad. Because your mom is not a carrier, she obviously has two normal genes and therefore all she could have given you was a normal gene. Your father could have given you a normal gene, or a PKU gene, so you have a 50% chance of being a PKU carrier.
Even if you are a carrier you do not have to worry about not eating asparteme. Those who have PKU lack an enzyme that breaks down an amino acid called phenylalanine, and they cannot break down phenylalanine. Phenylalanine is found in protein and asparteme, which is why those who actually have PKU must avoid asparteme and watch how much protein they eat. Carriers DO have the enzyme that breaks down phenylalanine. They DO NOT have to avoid protein or asparteme, because they do not actually have PKU, and their bodies break phenylalanine down normally.
You might be a carrier, then again you might not be. You should be fine consuming asparteme.