I have not had my period in almost a year. I was always not regular, and it could be due to my diet. Recently, I had a prescription of birth control filled and they tell me to take it the Sunday after I have my period. But, since I don't get my period would I be able to start taking it now anyway?
Has your health care provider addressed why you haven't had a period in almost a year? If not, then it would be wise to go back to the doctor and get to the bottom of that issue. Irregularity is normal (as weird as that sounds) for some women, but no period for a year is something that needs to be explored. There are several things that can cause a woman to miss her periods. Some of those things need to be addressed medically, so you should look into this further. Also, if your diet is the issue, then that is something that you can work on with help from your doctor (and maybe a nutritionist as well).
In terms of starting your birth control pills, you need to call your health care provider's office and ask them when you should start taking the pill (this will also give you the chance to ask about your MIA periods). They may want you to take a pregnancy test to make sure that you are not pregnant right now (not because the BC would harm a pregnancy, but because it would be a waste of money and effort on your part and because a pregnancy needs to be addressed if there is one).