T.V.
That's been very similar to my experience with it! I've had mine for almost 3 years. The first 2 years were that...spotting every 4 weeks, then 2 weeks, then back to 4 or longer...nothing consistent. Then all of a sudden, I had heavier periods, now nothing again!
I think it's pretty normal, but if it's making you crazy, call your Dr. I really think it's probably fine though. But if you have any big changes, make a call.