I had my period the second week of June, and I had unprotected sex around the 22nd and took plan B which made me start my period again on June 29th and it lasted until July 2nd.

On July 11th, I started Phendimetrazine which is a type of prescribed appetite suppressant. Then on July 28th I had unprotected sex again. Today is Aug 10, and I noticed I had light brown spotting, but no period. I thought I would get my period by Aug 2nd and haven't.

Is there a chance I may be pregnant, or is the reason I have not started my period due to starting phendimetrazine? If you take plan B do you normally skip the following month's period?