many website mentioned that it was good to take the uworld self assessment before i went for the real exams , so i took the exams ... for 2 weeks .. i took the test yesterday .. i wanted to practice more but i can't seem to start new blocks for self assessment ... can the uworld be taken only once even though i bought it for 2 weeks .. i am confused .. is it same with NBME self assessment or can it be taken multiple times .. help