I used to find this alot when reading. I think you can actually get books on the topic of psychic protection. I know it's probably just a way of asking the subconcious mind to create a bubble of loving protection around oneself to shield from negativity. You use alot of emotional energy sometimes when your read and psychic energy, i guess it's just part of the process and it can be draining like any other work. I heard about drinking water also and grounding. In my opinion very little can be done to avoid this at times.
I also do reiki which i find if you are trying to hard, you can drain yourself and actually block the healing. I wonder if it's the same with tarot, you drain yourself when you are not allowing the natural process of life to flow, when you are trying to hard. I've read alot on the law of least effort, it seems to be a spiritual law that the more we push the less happens, the more drained we become.
Start maybe to see reading as more of a pleasure more fun, i find when i'm trying to be perfect this happens. Try ease up on yourself maybe rather than trying to be right all the time. I'm just speculating that you have the similar problem as me, if not discard the above
I'm reading a book about toxic emotions at the moment. I do believe that some people are negative and surrounded by negativity, i'm learning how to protect against this so i will let you know. I find stopping reading helps, feeling drained is your bodies stress response, it's telling you to stop, slow down and reevaluate, come back to it later when you are more refreshed. Do you push yourself to hard perhaps?
Again alot here is speculation, so i apologise if it's not relevant. I'll let you know if i find anything further on the subject.
Good luck and let me know if you get any concrete feedback on this
p.s Another quick thought- the third eye is a muscle like anything else in my oppinion and needs to be used and as it does it stretches and i know after i use any muscle for too long i start aching, so maybe it's a sign of growth. I know after i horse ride i ache for days , but after doing it for months , i barely feel a strain. Perhaps the same applys with our psychic development.