Depending upon just how long the current problem has been going on it could be that your body is fighting off a peristent acute viral infection or if it's been going on for, say, several weeks, this could be Epstein-Barr/mono, which is fairly chronic in its acute phase (sounds contradictory, but is acute so long as it keeps acting up, then finally goes dormant). Much of what you describe could very well be EB/mono, and if it's been going on for two weeks or more there's a good chance that's what's happening. If this has been a week or less you're probably just having one of those passing viruses that can't quite get off the ground, or recurrent reinfection by exposure to someone at work or in the household who's either infected or carrying it.
If this has gone on at least two weeks you should be seen and have bloodwork done, including a monospot test done, as well as CBC and blood chemistry. If it is mono/EB, knowing this you can know what to expect (a drawn out, intermittent syndrome such as you're experiencing, followed usually by an equally long period of fatigue and energy dropouts) and can plan to concentrate more than usual on good nutrition, rest, planning shorter activities, etc. This is helpful because not knowing you can continue to be caught short as the infection flares and energy falls off. It can make life miserable for a month or more, with sometimes several months of slow improvement.
I hope this is helpful. Good luck to you and please follow up with us here as needed.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist