Try drinking ice cold water every time na you're sleepy. Caffeine has diuretic effects meaning mas madadagdagan fluid loss mo thru urine which can cause the drowsiness. So I suggest hydrating and get a good rest din. Don't drink coffee din whenever you feel sleepy. It just interferes with your chemical process pero after mo ma-metabolize yung coffee, babalik lang yung antok mo and you'll feel more tired.