I am day 8 now and my follicle size is 13mm,can i increase my follicle size up to 18mm?

Hi, I had follicular study 2 months back and at that time i had follicle arrest where they stopped at 14mm.And this time i am again going for follicular study and its my day 8 and my follicular size is 13mm.How can i increase my follicle size is that common or is it a serious problem.pls let me know....