Progress and Sudden Regression

Ive been studying throughout the summer taking PTs once a week and i was making good progress. I started at 158 in may, climed through the 160s throughout the summer and reached 171 and 174 two weeks ago. This past week and this week, however, I have dropped back into the 160s on three tests and dont know what to do, I feel like ive regressed, I was going to take it in september but now I think i have to delay it. What can i do?