Both palpitations and thyroid irregularity are often found, and often along with fibro-like symptoms, in late-stage Lyme disease. Your profile lists you as being in the Virginia Beach area, which is an area endemic for Lyme disease.
Most doctors will tell you that Lyme is easily ruled in or out by tests, but a growing number of patients and doctors are learning otherwise. You don't need to remeber a tick bite or a rash to have Lyme disease.
I don't know what testing or medical work-up you have gone through, but I would suggest you consider Lyme further before accepting just the fibro diagnosis. While many Lyme patients also get a fibro dx, the underlying cause of Lyme disease can be treated directly.
We have a Lyme forum here on MedHelp:
http://www.medhelp.org/forums/Lyme-Disease/show/148
The book "Cure Unknown" by Pam Wentraub and the documentary "Under Our Skin" are good places to start learning more about difficult cases of Lyme. Both the book and movie have easy-to-find websites with lots of free content.
Good luck and take care.