Well, it doesn't sound serious but if it goes on much longer, then I'd see your doctor. They really like girls to have a period every 3 months or so at the least unless you are very young. They may opt to do some blood work where they look at your thyroid function as well as your hormone levels. Both of those intertwine and both can make for very long cycles. Example, I had periods every three to four months when my thyroid was working slowly (called hypothyroid). What is your age if you don't mine me asking and is going to the doctor something you can do?
Ya, see your doctor. It's hard sometimes and everything is so intertwined in our health. Thyroid involves hormones, hormones involve thyroid. A thyroid issue can happen out of the blue too. By the way, weird question but it was related to my issue with thyroid --- do you have any depression? I had a low level of depression. Not enough where I didn't function but more like dysthymia. That is linked to thyroid issues. So, I'm just curious about that.