Transfer Factor - immunity from nature.

I advise you to do nothing. Let your body take rest. The body already has its own defense system if allowed to. I would advise you to go to bed early... yup, early to bed and early to rise makes a man healthy wealthy and wise... Never stay late at night; that's what primarily weakens our immune system. Avoid intoxicants or resorting to caffeine and  energy drinks (also nicotine = smoking). Stay as close to natural foods as possible. Eat honey and wild-caught fish (not the ones caught in rivers, though), sesame seed/oil, fresh orange juice or its skin boiled in water and mixed with natural honey. Hepatitis also causes tepidity. Check if your liver is in good shape (for its safety and proper functioning, avoid medication/drugs and chemicals in general as well as substitute sugars -- sweet-n-low, etc). Malfunction of the liver causes constant fatigue. If so, eat green peas to boost your liver. If none of the above applies to you and doctors' diagnosis is really valid (i.e. unjustified weakness in your immune system), I would rather apply it to "black magic". For unjustified sluggishness is one of the symptoms of real magic (beside nightmares, excessive fear and weakness in memory). If this is the case, get in touch with me (but only upon completing all medical diagnosis). I have nothing to do with magic, but I can only help you fight it through Islamic means, and upon your total submission to your Creator -- to Whom we seek refuge from all evils, both man's and Jinn's.

Try excercise to make yourself more active. I myself chose yoga. I once had a problem exactly like you do now. Feeling very tired, especially in the afternoon I sometimes had light fever. Body health check brought no result since there was nothing wrong. Then, I decided to do yoga. At first, I was totally exhausted because I was not used to it, but after 2 weeks, I felt very different. I no longer felt tired and also no more fever in the afternoon. Plus, I find it easier to sleep at night. Yoga really helps! Yes, it does. You should really try it. My friend even escaped from diabetes thanks to yoga. Hope you get better soon!

I advise you to do nothing. Let your body take rest. The body already has its own defense system if allowed to. I would advise you to go to bed early... yup, 'early to bed and early to rise makes a man healthy wealthy and wise'... Never stay late at night; that's what primarily weakens our immune system. Avoid intoxicants or resorting to caffeine and  energy drinks (nicotine included = smoking). Stay as close to natural foods as possible. Eat honey and wild-caught fish (not the ones caught in rivers, though), sesame seed/ oil, fresh orange juice or its skin boiled in water and mixed with natural honey. Hepatitis also causes tepidity. Check if your liver is in good shape (for its safety and proper functioning, avoid medication/ drugs and chemicals in general as well as substitute sugars -- sweet-n-low, etc). Malfunction of the liver causes constant fatigue. If so, eat green peas to boost your liver. If none of the above applies to you and doctors' diagnosis is still valid (i.e. unjustified weakness), I would rather apply it to spiritual reasons and negative energy.

Great pieces of advice!