My Son Is 10 Years Old And Has Had A

My son is 10 years old and has had a fever for two days. Yesterday it was 103, today it has gone down but is at 103 again. He just had diarhhea. My daughter had a fever as well, but it lasted two days and went away...though it remained low and I've had a fever but it has also remained low. I've given him acetiminophen (which seemed to help best) and alternated with ibuprofren (which doesn't seem to work as well). Could the medicines be hurting his stomach? He is complaining of pain in his lower abdomen.