My mom has had the same issues for over a year and a half now. None of her doctors have seemed to suggest anything outside the box and have just been treating her for RA, which all of the therapies, including methotrexate, have not been effective. I've suspected Lyme disease for her, and have done a fair bit of research on it. The tests for Lyme are not always accurate is the first thing I learned. You can easily get a false negative, as the antibodies are very difficult to detect. There is a Lyme disease forum here, which gives a lot of info on that.
But, if you're looking for other parasitic diseases that could cause your symptoms, then yes, they exist! My mom has had a lot of gastro issues (mostly diarrhea and dry heaves) additionally, so we're beginning to think somehow they are related to the myalgia and joint pain. She's also had massive chills and sweats too, not related to any fever. She traveled to Eastern Europe shortly before these symptoms began, so I'm beginning to think she may have ingested a parasite of some sort. My research has come up with various worms and such that can cause muscle pain, joint pain, and fatigue as well as other symptoms. Asia would definitely be a part of the world where you could easily get a parasite. Ask your doctor if they will do a stool sample and a blood test to look for parasites. But know that those tests can come back negative, since what they look for are eggs, and they may not be in that particular bowel movement.
There is a lot of stuff about online kits to "cleanse" yourself of parasites, but I have no clue if they are reliable at all. If you google "parasites humans asia" I'm sure you will come up with some specific suspects, but I warn you, they come with really gross descriptions and pictures! Definitely talk to your doctor though about a stool sample to look for eggs!
Thank you, kailau! You've been a great help!
Many ticks carry infections other than, or in addition to, Lyme disease. These include babesiosis, ehrlichiosis, bartonellosis, and more. Many of these so-called Lyme co-infections have significant symptom overalp with Lyme disease itself, but require separate testing.