I've had 4 periods in the course of 1 year, I've seen multiple doctors and no one has helped. What should I do?

I'm a 21 yr old female. Exactly one year ago I went off the pill, I had about two periods that were irregular in that time period. The Drs said t could be due to getting off the pill, I had two more periods that were very irregular. Out of the 12 months in this past year I've only had a total or 4 periods. What is wrong with me? I'm planning to go back to my ObGyn to see if we can figure out the problem. Yet I grow tired of waiting. What are u suggested tests/lab work/scans extra that I should take?