Hi My English Is Not O Good .My 7 Years

Hi my English is not o good .My 7 years old grand son being taking Ritalin for one year , for one week he being having hives but very litle ,goes and back but today ,he got a Lots and all his body , dr said because he has cough , when he was one year old ,he was taking antibiotics My poor baby got an awful rash after the medication , he was allergic three year ago dr gave antibiotic again and this time was very but .bad since then never had rash . His sister is taking antibiotic now . We are really worried about him we don't know what is goin on , his dr said is hive but aim think is the Ritalin , any advice please YYYY@YYYY