I got my period a week early while taking birth control pill

I have been taking birth control since I was 15 and I'm now going on 28.  My last birth control pills were Alesse and I was taking those for about a year until I started getting my period 1-2 weeks early (while still taking the pill).  My doctor said it might be my body getting use to the pill and to maybe try a stronger pill, so now I am taking Yasmin.  I am just finishing my 3rd month on Yasmin, and got my period a week early again. The first two months everything was regular and normal.  I have been taking all my pills on time and everyday.  I'm just getting frustrated because I'm basically having my period half a month when this happens.  Also, I have taken blood tests and PAP and everything has been coming back normal.  Can anyone give me tips or suggestions on what I should do or ask my doctor now? (made an appt to see him again this week).  Only thing that I have changed in my lifestyle is I quit smoking and started exercising, but I just started doing this a month ago and this started happening in January.

Please help!  Thanks =)