It could definitely be burn out! I took the January exam and completely burnt myself out doing what you were doing, by taking 2-3 practice tests a week. In hindsight it was the worst thing I could have done because it shot my confidence and I ended up performing way poorer on each PT than I was used to. I thought the best way to estimate my score was to increase the test frequency, but it just proved to me that burnout is indeed real and it can definitely have some detrimental effects your performance.