This is going to be long, sorry.
I have just found the thread on ME / CFS and have spent the last few minutes crying my eyes out because it is like finding the missing part of a jigsaw 
. I'm sorry if this is long but I am just trying to work out what is going on and find some answers.
I have been going through the same cycle of illness/exhaustion for years now, and I am at my wit's end.
In my 20s - pre kids - I worked in a very full on job, involving long and unsociable hours. I was very successful and capable, and rarely ill, but looking back now I was holding the illness and exhaustion at bay by getting a lot of sleep at weekends. I used to spend at least one day - sometimes both days - each weekend in bed all day recuperating from the week. If I didn't do this, I was prone to cystitis and kidney infections and would completely lose my appetite and rapidly lose weight, so I sort of instinctively knew (without ever verbalising it to myself or anyone else) that I needed more rest than most people in order to function normally.
After having my first child, I got PND. I went back to work about the time the PND fog was starting to lift, but I was plagued by 'minor' infections and illness (migraine, chest infections etc). I also had a very stressful and horrible experience with bullying at work and eventually left my job (which stunned everyone, as I had always been such a dynamo and career-driven person).
From this point onwards (almost exactly 5 years ago) I have been going through this depressing cycle which is ruining my career and having a major effect on my relationships .
I take on a job or a course, I am functioning well and doig really well at whatever the project is...then I get ill. Really, totally wiped out ill and exhausted.
I left one job when the initial 6 month contract lapsed (even though they would have happily renewed it) because I got tonsilitis followed by flu and then had some sort of post viral exhaustion (the whole thing went on for about 6 weeks) and just lost all energy and heart to do the job. I then embarked on retraining, which I just about completed, despite having to take 8 weeks off mid year because of recurrent tonislitis.
I then got pregnant with my second child and spent most of the pregnancy with flu, colds, sickness, aching body etc.
Since she was born I have had two short contracts which I have chosen not to renew because towards the end of each contract I have become so exhausted and ill.
I have been in my current role (again, a 6 month contract)for 2 months and have been off sick with some sort of flu virus for a week. This is the first day in seven days that I have been able to lift my head off the pillow. I am sure that my boss is not impressed .
This is doing my head in. I am scared that I am going to make myself unemployable , not to mention sick to the back teeth of being ill.
One thing that really struck a chord on the ME thread was when someone said that if they had a busy day they thought to themselves 'I am going to pay for this tomorrow'. That is my life .
What should I do? The GP says he is going to refer me for an op to get my tonsils out after I got a Quinsies (sp?) at Christmas, and that I need to take vitamin supplements, but he was sniffy about ME/CFS and I don't know if I have the energy to push for a diagnosis, or what I would really be doing it for.
I am just at a loss, really, and feel so alone. I feel like nobody understands and that people just think I am a flake .
Btw, when I am well, I exercise moderately (pilates and aerobics and swimming), I eat fairly well, don't smoke, drink moderately and, touch wood, have never had any serious illnesses.