able to life 250 lbs+ to not being able to lift my 4 yr old?

Hello I am a 28 year old male im 6 foot 1 and 225 pounds about 4 weeks ago I went to bed feeling normal and woke up feeling weak in both arms and legs (went from being able to life 250 lbs+ to not being able to lift my 4 year old) so after a week of this I went to the doctor who had blood work done but everything came back normal...3 days after that I went to the ER they did blood work ( also checking for mono and lime) urine lab (no muscle breakdown) and a cat scan of my brain and xray of my chest ...all came back fine..but still barley able to carry myself ..so my dr sent me to a neurologist who had a mri of my brain and spine done both came back normal... since then other things have started to happen like extreme head pressure and not being able to sleep through the night (I sleep for an hour and am up for and hour all night long and my mind races all over the place when i wake up not just about my health but about anything from the day) so my dr wanted more blood work this time covering alot of odd ball chances and alot of stds and a cat scan of my abdomen all came back fine...for being so healthy i feel like im dieing ...2 days ago i went to another ER at a different hospital they did the usual blood work and urine and also did a EKG on me everything came back normal except my potassium levels where low ( 3.1 suppose to be 3.5+) they gave me potassium pills and sent me on my way ...I haven't improved at all over 4 weeks just added new problems any advice to ideas on what I could be suffering from would be greatly appreciated .....I have a 4 year old who doesn't understand why daddy doesn't want to play with him any more and it breaks my heart if you have a thought even a long one please respond im desperate