Diet and nutrition symptoms and conditions

My daughter has taking singular for about 3years. Her doctor put hersingular for allergies when she was five years old she is now 8 years old. There was no problem at firs.It took about 6 months before started seeing her change .She has a lot of hate toward her mother, sister, father.She has mood swings saying she hates us sometimes she wishes we were dead. She is all the time hitting her sister.We took her off of them for about a week and she changed toward everybody she was the best kid you could ask for, but her problems started with her allergies again so we had to put her back on them. We took her back to the doctor and they say there is no other allergy medicine that will work her. She has to be on something or she will run high fevers for weeks plus lots of nose problems and watery eyes. She has complains of a lot headaches more than any other kid would