L.,
I am a nurse who had worked in ob/gyn and can tell you that every time you do something to alter your hormones, there comes the possibility of creating irregularities in your cycle. LoEstrin is a low dose pill that can certainly cause you to miss a period every now and again. Also, when just starting a new pill, it takes your body about 3 months to adjust so during that time period you can experience bloating, spotting or no bleeding at all. There are hundreds of birth control pills out there and its hard for a doctor to know which one to pick for each patient - sometimes its just plain old trial and error. I would express your concerns to your doctor and they will advise you of your options regarding this and other birth control pills.
Hope this helps! Take care,
T.