I've been taking low dose Amatryptyline for two years for my fibro and it stopped working a few months back. I realised I was having chest pains within an hour of taking them at night, and still no sleep was forthcoming.
Saw the GP, who is lovely, but honest in her lack of expertise in this area. She basically said they've stopped working, it happens, but asked me what she should prescribe next. 
I saw a Rheumatologist for the original diagnosis, privately, and do not want to see him again. He threatend me with court for non payment of his bill when he had been paid by Bupa, just had bad accounting practices and was chaotic. When I finally got it sorted, he was massively apologetic, but I want nothing to do with him now. The problem is, the gp said he will know the next med on the list when the amatrypyline stops working.
I think he said he would try Gabapanton or something like that. If I can't figure it out, I will ask for an NHS referral to a rhumy, just am feeling desperate. Have had no sleep for six days, palpitations are coming back.
Was wondering if anyone with fibro had any ideas? Thanks x
PS I know she should look it up, it's just that she gives me credit for knowing more about this condition than she does and I actually stopped researching it as the symptoms were freaking me out.