My eldest son has constant aches and pains, depression, feelings of exhaustion. He has been like this for 10 years or more. He had x-rays, blood tests, scans, etc., which all came back normal. Finally, after various illnesses were ruled out, he's been told he's probably got Fibromyalgia. He is on antidepressants (the 4th type he's tried, which seem to suit him now), and strong prescription-only painkillers.
My son has to work full-time (10 hours a day, over 4 days, plus 90 mins each way on buses)so that he can pay for his children(he doesn't live with them), his rent, bills, etc.
I think some people dismiss Fibromyalgia as being "in the mind", but the physical pain is real. It can be very debilitating, and a couple of years ago, he was so bad with it, he had 3 months off sick from work (his employers are a huge company and they look after their staff very well), but he can't keep doing that.
When my son sees his children (6yrs and 3yrs) at weekends, he chases them around, swings them about, does all the rough and tumble stuff.... and then he's in lots of pain for days afterwards.