23 yo no history of high bp or familial cardiovascular problems. sharp headache on side of head upon ingesting caffeine. aneurysm or brain tumor?

Unlikely: Much more likely that you are sensitive to caffeine. If it persists, talk to your doctor.

Sensative: Caffeine is a vaso constrictor (makes vessels smaller). You may be very sensitive to caffeine or you may be taking in more than you should (too much coffee in one day). I would reduce my caffeine intake and be aware that you may get a headache from not taking in as much as you used to. Tea has less caffeine and you might try tea if you need the caffeine.

Allergy reaction: Head ache , migraine is very common allergic reaction to caffeine, see your doctor, stop drinking coffee tea and cola which contain caffeine , before blaming aneurysm, and brain tumor.

Neither likely : At the age of 23 it is unlikely to be either of those and most likely a side effect of the caffeine. Try and cut back in the amount of caffeine you have and see if it improves the headache.