I haven't had a period since 16 y/o.

I am 21 years old and started my period around 12 years of age. I had a regular period for about 3 years until I began taking birth control at 15. At this time, my period stopped and my doctor told me it was due to my birth control. I switched to a different birth control at 16 and it gave me a regular period, but it was giving me acne so I switched again to another kind. Since then, I have not had a period. (Not even spotting) After going to an OB GYN, she explained that it's important to have a period a few times a year, she put me on a birth control with added iron and more hormones (I think?) It's been three months and I still have not had a period or spotting. I am wondering if there is maybe something more to this than just birth control. I have taken Junel, Loestrin plus Fe (caused period and acne), Loestrin, Microgestin 1/20 Fe 28s, Microgestin1/20 21s, and now Microgestin 1.5/30 Fe 28 (I can't remember exactly when I changed to some of these)