I have Hashis and primary Sjögren's, which was first misdiagnosed as RA. RA usually starts in small synovial joints of the hands and feet - which isn't the base of the thumb or palm - not your back or hips or other larger joints. These joints really can hurt due to inflammatory arthritis of Psoriatic Arthritis, Ankylosing Spondylitis, Lupus or Sjögren's though. Osteoarthritis less likely at your age.
I had these with lower back ache, hip pain and knees and wrists excruciating and it turns out it that these were all Sjögren's related secondary osteoarthritis and tendinitis, rather than RA. But it imitated RA so well (as Lupus can do too) that two rheumatologists and my GPs were all convinced!
Re bloods - sadly no one tested my ANA for Sjögren's or Lupus until I was a few years into DMARDs and steroids - when they all came back inconclusive. My Rheumatoid Factor, inflammatory markers CRP and ESR/ PV were all elevated though - and still often soar. Once off everything my ANA came back clear positive and I was given a lip biopsy last year which was 100% positive for Sjögren's.
There is a tendency for doctors not to test for Sjögren's in anyone under 40 (which is nonsense!) but most have either positive RF or ANA (can be run by GP) and then a rheumatologist can run the more specific panel of bloods for RA, Lupus, Sjögren's etc once you've been referred. Definitely don't just blame this on Hypothyroidism please! There was a young Olympian Judo player speaking about her diagnosis of primary Sjögren's on radio 5 live the other day and other young people too.