I have been on Yasmin for 2 years now, I've never ever had any problems with it. I've always started when I was supposed to, I haven't skipped any pills, I've taken them like I should. Well I've started my period 8 days before I should have started. Its a weird period though. I had very light spotting on day one and two, only noticable when going to bathroom, and then it got a bit heavier day 3, but not at all like my normal period heavy, at all. On day 4 and on day 5 very light, and yesterday nothing whats so ever, and this morning a very light brown discharge. My normal periods only last 3 to 4 days really heavy, and now this is happening. I've called my doctor and all the nurse said is just monitor it. I was on antibiotic for 2 days and took a double dose of it each day (4 pills total) about 3 weeks ago, could that have caused all this? I also took cough medicine, and cold medicine about 3 weeks ago as well. I should start my period this coming Tuesday since I'm on my sugar pills...could I possibly be pregnant? Thanks for your opinions. :)

That same exact experience happened to me a few couple of months ago. I was taking OTC lo (also for 2 years) and, like you, I always took it on time, never skipped a pill, and my periods were always predictable. Than one day just out of the blue it came a couple of days early, than it stopped, and it went back and forth between light pink discharge to brown till I finally got my full period about 4 or 5 days later, and the period was lighter than normal.
I was really worried but didn't want to make an appointment till I was sure that there was something wrong. I also took a pregnancy test which was negative, so I figured it was nothing to worry about.

After that incident my periods went back to normal and were predictable as before.
I don't know exactly why that would happen, but if you're taking them correctly I'm sure you have nothing to worry about.
It also could be that you've been taking other medications as well, but I guess this kind of stuff happens sometimes.
If you're really worried you can always take a pregnancy test, but I'd just wait for the next period which will probably be normal.