Hi, welcome to the forum, sleep is quiet important and should not be reduced at the expense of study. Optimal duration of 6-8 hours is sufficient. Your symptoms are due to Shift work. As you force yourself awake to study and thus over many days sleep disorders develop. Even uninteresting topics for study can make you sleepy.
The sleep problems can be resolved by transferring from the night shift or by adopting a daily sleep routine that is consistent seven days per week.
You can take tea or coffee which is stimulants, before start studying.
Study in bright light.
Take walk in between.
Do not read continuously, give breaks.
Take care and regards.
You don't say at what time you try to do your studying, but either way, I would recommend you start earlier in the evening, and don't eat a heavy meal before, just eat something light...enough to hold you until you are finished studying.
You may need more stimulation while you're studying. I'm not sure if you're a multi tasker, or if you need that complete and quiet silence to learn the material you're studying... but either way it seems like you're not getting enough stimulation to keep yourself from getting sleepy. Maybe try a noisemaker with like waterfall sounds (or white noise) or something like that, if you're familiar with those devices. Sometimes I'll put the radio on the AM channel, because while it's not very stimulating, it may keep your mind a little more in tune to what you're doing. Listening to music on a low volume setting can help too. Try to get more interactive with what you're studying - writing more notes or making flashcards or something. Do more than just reading. Hope any of this helps! good luck!