Re: Probably just a virus but...
Yes, I had a similar thing to this, had a virus in mid December which came on suddenly as shaking and nausea, followed by a fever, followed by feeling weak, wiped out and tired. The fever came back over the next couple of weeks mildly and I felt tired all the time but my head hurt and my IBS was really bad so I couldn't sleep. I saw my GP and she said she'd seen a lot of people with similar viruses that were making them feel very miserable.
Look after yourself. Get a reasonable amount of sleep but also try to get outside and do some gentle exercise. Eat healthily and drink plenty of water and you should gradually improve. As has been said above, you'd be sure to have more symptoms if it was something serious.
__________________
"Every day, every hour, I wish that I was bullet proof"