Should i continue taking these medicines?

my doctor prescribed 3 medicines:an antihistamine (once a day), a decongestan (3x a day) and and antibiotic-amoxiclav(3x a day). he said i should take these for one week plus an inhaler for my asthma. now im getting nauseous, stomach upset and dizziness. i cant concentrate on studying. but i still have phlegm and decongested nose. should i continue? what do you think? another thing the meds. are quite expensive.