Your story is so typical of what I see here on this forum. Misdiagnosis after misdiagnosis. I went 10 years of being told that it was psoriasis, excema, ringworm, scabies, fungal... on pill after pill, cream after cream.... before it was finally diagnosed as FD.
The problem is, FD is a rare condition... so GPs and even many Derms have no idea what they are dealing with.
I've had no experience with arm or torso folliculitis, but I do know that its a bugger of a disease that CAN be managed.