to have a splitting headache:
this means your headache is very bad and painful
to have a migraine:
this is a very bad headache; you have a pain behind your eyes and you might feel sick
to have a temperature:
this means that your body temperature is higher than normal. Your forehead probably feels hot
to have an upset stomach:
this is a general way to describe a stomach ache, usually when you also feel sick or have slight diarrhoea
can/can't keep your food down:
this means that every time you eat, you vomit