Pls i am esperiencing severe headache and drowsiness what medication should i buy?

See a doctor: For right now get some tylenol (acetaminophen) then get to a doctor. Without more information it's hard to know what's going on but a "severe" headache is a symptom that merits a real evaluation. It could be a migraine, it could be muscle spasm or it could be any number of problems. Get checked out!

See a doctor first: Drowsiness is an unusual accompaniment of severe headaches, such as migraine. It suggests that there may be a serious underlying cause, which needs to be investigated, possibly with blood tests and an MRI scan. If those are normal, then it is most likely a migraine headache and it can be treated with Aspirin (with magnesium) or sumatriptan.