Physical pain and weakness/lethargy are very common symptoms of depression (when you're in your low stage during the bipolar disorder)
In some cases as a last resort, some psychiatrists prescribe Adderalle to the client to help with the psycho motor retardation.
Other things you would like to check are your thyroid function and vitamin D level and iron by a blood panel test.
Also, if you have not had a sleep study specifically, you may consider having one. Circadian disturbance can make you feel very tired/exhausted. Weekend immune system can cause you to feel more pain and be prone to illness.
It can come and go (you feel as though you don't even have energy to lift your coffee cup to your lips) You may feel pain in your back, neck, and your legs and arm may feel very weak like if you have Mono or the flue. You may have a throbbing headache. You do not have to be anxious during this experience. You could have just woken up and feel it.
Did your sleep study confirm if you have the disorder or not? It can mimic the symptoms of depression if you have it.
Now, you would most likely feel this way when you're in your depressed stage.
What had helped me is supplementing with vitamin D, L-carnitine, amino acids complex, use of blue spectrum LED light and you may also check truehope.com