As @Isaiah_40_31 says, there are members who’ve had both, the symptoms are similar. There have been a few discussions, here’s a link:
The Importance of Diagnosing Ernest: A Crucial Study - General - Living with Eagle
Autoimmune issues do seem to be common, my personal (not medical!) opinion is that the inflammation caused by calcified ligaments maybe triggers it…
There have been lots of discussions about flare ups & the answer is we don’t know what causes them, I’m afraid! It’s very common & seems to be no rhyme or reason why symptoms flare or disappear 
I hope that you can get a CT & a definite diagnosis.