Period on birth control..what?

I hope this isn't too much info.. anyway - I've been on birth control for almost 3 months now and today ( 5 days before I'm supposed to take the sugar pills) it seems like I'm getting my period (spotting, slight cramps etc).. I'm wondering why this is happening now.. it was exactly on time last month and I thought that the longer I was on bc the more on time it would be! Anyone have any thoughts on why this could be? Thanks

Don't worry, spotting in between periods is very common in the first 2-3 months of taking birth control pills. If it continues past 3 months you should see your doctor because your prescription may need to be adjusted.

Thanks for your reply.  It just seems hard to understand because since everything went perfectly last month!