I Have Arthritis Pain I Have Been A Whole 30

I have arthritis pain I have been a whole 30 diet/ paleo for a year when I am very strict with my diet I loose weight and feel better. But lately I'm slowly gaining weight again and my pain is returning. I went my dr for a blood check to see if my thyroid was good they only did basic tests and everything was in the normal range what kind of dr can I see to do a special thyroid test