How to get treated for mental fatigue and tiredness?

Hello doctor,

I finished my MBBS and attempting to get a PG seat. I have the below mentioned problems for more than eight years and hence I am unable to get a PG seat. I am taking tablet Venlafaxine 300 mg for past seven months. Three weeks back, as I have few clinical symptoms of hypothyroid my physician suggested me to take tablet Thyroxine 25 mg. I feel 40% happy and better after using the tablet Venlafaxine. But that is not enough to crack the PG seat. My first issue is mental fatigue. When I study more than 4 hours or a new topic I feel more tired and have difficulty to wake up. I cannot squat or keep the hand raised or lift moderate weight for few seconds above the shoulder for some time. Lack of concentration or difficulty to mingle for some days after this attack. Back muscle ache and always seeking support for sit and do work. Easy propensity to go for sleep in morning hours during OP times. Also, afraid of PG due to this problem as sleep may attack while reading also. I get sleep while read and jump to some other topic in few seconds after coming out from that nap . If I read when I am alone then more tendency to go to sleep. Finally, more waste of time as I do not get sleep. If I go without sleep, more tiredness and severe discomfort. This fear gradually decreases over some days and again I will study and same steps are repeating. During morning times I hesitate to stand for some time and avoid those situations. Sometimes this becomes a problem as emergency patient needs my standing attention. If I read aloud less sleepy than when read inside but study rate is slow. Morning times feeling 40% weakness or loss of interest or loss of energy or sleepiness. Also if I stay alone the work or study productivity is not increasing. Sometimes somebody should stay with me to finish my tasks. Is this a kind of dyslexia? The second issue is physical fatigue and myalgia. Sometimes the body will be ready to meet the demands and work for more time, and I demand more work from staff at that time and other time I am in town and cannot ask others to work even too. Regarding neck pain, if I do any work on a laptop in my lap within 30 minutes, I am getting neck pain (last 5 years). Also, the same with a gold chain around the neck and legs in sitting position. Legs feeling so tired. So the fatigue, neck muscle strain, leg muscle ache while semi-stand or squat can give us the best guess to diagnose the problem. Burning of eyes is also observed during studies or excess physical work or excess protein content taken. I am suffering from on and off Plantar fascists of left foot from last 7 months. Why is it not decreasing fully? Please help.