Period is regular. I do in this case.

Hello my periods are regular i get them every month but aftr taking duphaston for 2 weeks and later when i do  tests as told by Dr.. Today i did which is negative and now i  have to wait for periods then my cycle gets disturbed yesterday was my last day of Duphaston. My last month cycle day was 10th Aug.. According yo that today its my 31st day.. But from today i will not take  duphaston as i completed my 2 weeks course and did test too..now according to dr if test is negative i need to wait for periods to come Naturally but due to which my cycle length would go to more than 35 days or so..what should i do in this case..pls hlp.. Whole cycle gets disturbed could not track my ovulation too...pls hlp.. Dr suggested me this Duphaston course for 3months..this is my 1st month of course...advice what should i do stick to dr advice or just stoo tablets from coming cycle and visit dr for conceiving in other way..