This sounds like me. I would go 6 months without a period. I called my doctor, and she called in a prescription (for estrogen, I think) to start my period. I wanted to say, I'm not complaining, I just want to make sure nothing is wrong. When I saw her for my annual, I told her how this happened again. She called in another prescription, this time with refills.
She was not concerned at all. But she told me that the reason she wanted me to take the meds is that if I go too long without a period, when I do have a period it can come on really, really strong. And one time it really did. I was sitting at my desk too long (about an hour!) and had to run to the store and buy new pants! Nothing like that has happened since junior high!
My doctor wants me to have a period at least every 3 months, so she said if it's getting close to 3 months I should take the meds. I had to take the meds twice (I think) since I saw her last fall, but the past 3 months I've had a period.
I would keep asking your OB, just to be safe, but I do know what you mean. I recently turned 40, so maybe this is par for the course. My husband was hoping it was menopause, because we've decided we're done having kid and he doesn't want to have to do anything about it on his end. Hhmmm, he might need to rethink that!