Why did I score better on the first 3 BB tests than ones after that?

I’m super discouraged…my score on each of the first 3 BB tests was higher than the previous.
When I took the 4th BB test…my results dropped about 250pts and have been decreasing ever since.
This doesn’t make much sense to me and I’m not even sure what I’m scoring now?

Highest of first 3 tests: 2100 with 800 (or 49 MC) English, 690 (or 56 raw) Critical reading, and 630 (or 40 raw) Math
Average of tests after first 3: 1870 and around 41 MC english, 54 raw CR, and 33 raw Math

Makes no sense…I have been studying too. I miss more questions on the tests after the first three.

I am scheduled to take the SAT tomorrow and after having completed my worst test so far today, I’m seriously rethinking that. Isn’t it pointless to take it just to get a low score?